Environment variables having wrong character encoding

I have defaultTargetPanel and packs are installing to this location:
<file override="true" src="C:\kiln\installer\install_files\launcher\MinecraftEdu\" targetdir="$

" os="windows"></file>

It works fine, BUT if username contains special characters, like ä or ö, it converts them into: ,,
So when my username is kylmäoja, special characters show as ,, and installer fails.

I tried inputting direct path to my appdata folder (without environment variable) and it worked, so environment variables have wrong encoding data.

This has been tested with Windows XP and Windows 7 on separate computers.