taken from the original google code issue:
Taxon names that differ only in the presence/absence of diacritic marks ought to be treated as spelling variants rather than as separate names.
4377003 Achnanthes plonensis
4920773 Achnanthes plönensis
5977298 Pseudopanthera oberthuri
1954573 Pseudopanthera oberthüri
I think there are quite a few of these. There are also many cases where the names are also obviously synonyms but the spelling difference reflects a transliteration of a diacritic, for example:
2630477 Achnanthes ploenensis