I just found something strange in my logs as I didn't check them for some time.
I updated today to 188.8.131.52 from 184.108.40.206 so I did view some logs by the way and it seems that since January 2013 Polish letters are saved as normal letters. For example 'a' instead of 'ą', 'z' instead of 'ż', 's' instead of 'ś' etc. The only letter not converted is 'ó'.
The new version also converts those letters.
I'm not sure, but maybe there was some Windows update that broke it. And it could have something to do with UTF-8 coding.
Here are suspected updates: http://i.imgur.com/w96Pof2.png
I didn't reinstall the system and didn't update Anuran since 2011, so I don't know what else could it be :/
I use Windows 7 x64 English version set to Poland in regional settings.
I'm going to install system on new disk soon and will post some updates then.