UTF8GreekAccents filter has several issues

The issues can be classified in two categories.

1. Greek accent not filtered out
2. Non-diacritic character filtered out that shouldn't be

In #1 the accent is    U+0345   ͅ    COMBINING GREEK YPOGEGRAMMENI
In #2 the character is U+2019   ’   RIGHT SINGLE QUOTATION MARK

The latter is NOT a Greek accent. AFAIK, there's no valid reason to filter this out.

For reporting details, please refer to the recent discussion in sword-devel.

For detailed background, please refer to Greek diacritics

In addition to these two particular issues, there's the greater concern about the filter not having a restricted scope. Because some Greek accents are not particular to Greek but general combining characters for other languages too, when the filter is applied to non-Greek text, it removes diacritics that should be retained in that context.

Furthermore, because the filter makes use of Unicode Normalization to NFKC as a prelude to removing the combining characters, it has the side-effect that some unusual codepoints are not restored afterwards on account of the fact that decomposition for some codepoints is not reversible.

Example: U+00BE VULGAR FRACTION THREE QUARTERS ¾ becomes 3/4

NB. "Affects Versions" seems to be out of date in the CrossWire Tracker.
My observations were made using Xiphos 4.0.4 and diatheke version 4.7