The problem is that I can't understand myself the system when it happens. Usually when I'm creating new Panel, it is in Windows-1257 code page, but not always. I'm using non-ascii characters in label captions, so there is impossible to compile project (wxWidgets is in Unicode mode). So I'm changing those files manually to UTF8, but sometimes CodeBlocks is changing files back to Windows-1257 by saving.
I started developing my project in Linux but now continue in WinXP. Some of project files are in DOS some in UNIX format. All .wxs files are UTF8 and UNIX. There is no problems with my other projects, but I didn't use non-ascii characters before. All files in my other projects are in UTF8 format.