I have some problems with diacritic mark "á" in 2 items.
Almost every girl name in the Czech rep. ends with character -á, more exactly -ová. Just in one case, MPE can't display it and sync it like question mark with the phone and Thunderbird.
MyPhoneExplorer is not fully Unicode-Compatible. this means that you have to set the right system-charset on your PC that the national chars are displayed correctly. Please also use "normal" fonts like "Microsoft sans serif", "Tahoma" or "Segeo UI" to ensure that this character is listed in the font-file.
A short look into windows chartable showed me that á is listed in charset "Westeurope" and "Middleeurope" as ASCII-Char. You can change the system-charset in Control-Panel->Regional settings, the setting is called something like "System-charset" or "Charset for Programs which do not support unicode".
I tested it on my PC (set to austrian charsets) and everything works also with á - also the sync with Thunderbird in both directions.
There is Control Panel/Regional Settings/Administration/Language for Programs which do not support Unicode.
It is set to Czech and doesn't work in MPE, I didn't check Austrian, but it would not have been solution. It could even cause other problems in other aplications