Consider the frog genera Philautus and Raorchestes. The latter was described in 2010:
A ground-dwelling rhacophorid frog from the highest mountain peak of the Western Ghats of India (2010)Current Science (Bangalore) 98(8): 1119–1125. http://bionames.org/references/e0ab13cbb8bc8b3627bb53e88e7641a9and contains a number of species previously in Philautus. The GBIF classification for Philautus still has these species, which means that these taxa appear twice in the GBIF data portal (associated with different occurrences).
To gauge the scale of the problem I've done a crude pairwise plot of species names in the two genera. In the diagram below a dot(●) appears if the species name in the corresponding row and column is identical. The diagonal corresponds to comparisons of a species name with itself.
Note the ●'s that appear off the diagonal. These are species in Philautus and Raorchestes that have the same species name (e.g., Philautus glandulosus and Raorchestes glandulosus. The off-diagonal dots indicate taxa that are duplicated.
● ● Raorchestes anili
● ● Raorchestes annandalii
● ● Raorchestes beddomii
● ● Raorchestes bobingeri
● ● Raorchestes bombayensis
● ● Raorchestes chalazodes
● ● Raorchestes charius
● ● Raorchestes dubois
● ● Raorchestes flaviventris
● ● Raorchestes glandulosus
● ● Raorchestes graminirupes
● ● Raorchestes griet
● ● Raorchestes gryllus
● ● Raorchestes longchuanensis
● ● Raorchestes luteolus
● ● Raorchestes menglaensis
● ● Raorchestes munnarensis
● ● Raorchestes nerostagona
● ● Raorchestes ochlandrae
● ● Raorchestes parvulus
● ● Raorchestes ponmudi
● ● Raorchestes sahai
● ● Raorchestes shillongensis
● ● Raorchestes signatus
● ● Raorchestes terebrans
● ● Raorchestes tinniens
● ● Raorchestes travancoricus
● ● Raorchestes tuberohumerus
● ● Raorchestes viridis
● Philautus abditus
● Philautus abundus
● Philautus acutirostris
● Philautus acutus
● Philautus adspersus
● Philautus albopunctatus
● Philautus alto
● Philautus amboli
● Philautus amoenus
● Philautus andersoni
● ● Philautus anili
● ● Philautus annandalii
● Philautus asankai
● Philautus aurantium
● Philautus auratus
● Philautus aurifasciatus
● Philautus banaensis
● Philautus basilanensis
● ● Philautus beddomii
● ● Philautus bobingeri
● ● Philautus bombayensis
● Philautus bunitus
● Philautus caeruleus
● Philautus cardamonus
● Philautus carinensis
● Philautus cavirostris
● ● Philautus chalazodes
● ● Philautus charius
● Philautus cinerascens
● Philautus cornutus
● Philautus crnri
● Philautus cuspis
● Philautus decoris
● Philautus dimbullae
● Philautus disgregus
● Philautus dubius
● ● Philautus dubois
● Philautus duboisi
● Philautus erythrophthalmus
● Philautus eximius
● Philautus extirpo
● Philautus femoralis
● Philautus fergusonianus
● ● Philautus flaviventris
● Philautus folicola
● Philautus frankenbergi
● Philautus fulvus
● Philautus garo
● ● Philautus glandulosus
● Philautus gracilipes
● ● Philautus graminirupes
● ● Philautus griet
● ● Philautus gryllus
● Philautus gunungensis
● Philautus hainanus
● Philautus hallidayi
● Philautus halyi
● Philautus hazelae
● Philautus hoffmanni
● Philautus hoipolloi
● Philautus hosii
● Philautus hypomelas
● Philautus ingeri
● Philautus jacobsoni
● Philautus jerdonii
● Philautus jinxiuensis
● Philautus kempiae
● Philautus kempii
● Philautus kerangae
● Philautus leitensis
● Philautus leucorhinus
● Philautus limbus
● ● Philautus longchuanensis
● Philautus longicrus
● Philautus lunatus
● ● Philautus luteolus
● Philautus macropus
● Philautus maia
● Philautus malcolmsmithi
● Philautus maosonensis
● Philautus medogensis
● ● Philautus menglaensis
● Philautus microdiscus
● Philautus microtympanum
● Philautus mittermeieri
● Philautus mjobergi
● Philautus mooreorum
● ● Philautus munnarensis
● Philautus namdaphaensis
● Philautus nanus
● Philautus narainensis
● Philautus nasutus
● Philautus neelanethrus
● Philautus nemus
● ● Philautus nerostagona
● Philautus ocellatus
● ● Philautus ochlandrae
● Philautus ocularis
● Philautus odontotarsus
● Philautus oxyrhynchus
● Philautus pallidipes
● Philautus papillosus
● Philautus pardus
● Philautus parkeri
● ● Philautus parvulus
● Philautus petersi
● Philautus petilus
● Philautus pleurotaenia
● Philautus poecilius
● Philautus polillensis
● ● Philautus ponmudi
● Philautus poppiae
● Philautus popularis
● Philautus procax
● Philautus quyeti
● Philautus refugii
● Philautus regius
● Philautus reticulatus
● Philautus rhododiscus
● Philautus romeri
● Philautus rugatus
● Philautus rus
● ● Philautus sahai
● Philautus sanctipalustris
● Philautus sanctisilvaticus
● Philautus sarasinorum
● Philautus saueri
● Philautus schmackeri
● Philautus schmarda
● Philautus semiruber
● ● Philautus shillongensis
● ● Philautus signatus
● Philautus silus
● Philautus silvaticus
● Philautus simba
● Philautus similipalensis
● Philautus similis
● Philautus sordidus
● Philautus steineri
● Philautus stellatus
● Philautus stictomerus
● Philautus stuarti
● Philautus supercornutus
● Philautus surdus
● Philautus surrufus
● Philautus tectus
● Philautus temporalis
● ● Philautus terebrans
● ● Philautus tinniens
● ● Philautus travancoricus
● Philautus truongsonensis
● ● Philautus tuberohumerus
● Philautus tytthus
● Philautus umbra
● Philautus variabilis
● Philautus vermiculatus
● ● Philautus viridis
● Philautus vittiger
● Philautus williamsi
● Philautus woodi
● Philautus worcesteri
● Philautus wynaadensis
● Philautus zal
● Philautus zamboangensis
● Philautus zimmeri
● Philautus zorro
Why does GBIF have duplicate frogs? As for the gibbon example, the names come from different sources, and GBIF doesn't have access to (or doesn't use) data that tells it that the names are synonyms. In this case there is a clash between the Catalogue of Life, which doesn't recognise Raorchestes, and IUCN Red List, which does. The end result is a mess.
We clearly need better tools for catching these problems. We also need a decent database of taxonomic names and synonyms. The Catalogue of Life is, frankly, grossly inadequate in this respect, especially for vertebrate taxa. Increasingly it's becoming clear that the classification underlying the GBIF portal needs some serious work.
