The ini file gets written correctly, as it seems, but the file size is not updated, if the new file is smaller than the old one. This results in an ini file, that contains some of the old content at the end. I'll attach 2 files, to make this clear.
Steps to reproduce:
1) Set up BASS to override the global volume settings. Hit Ok → File gets written. File has x (=550 for me) Bytes and is correct.
2) Edit the game and disable "Override global volume settings". Hit Ok → File gets written. File still has x Bytes. It now contains the new content, which is shorter than the old and some of the old content that "fills" the x Bytes.
3) ScummVM will not start anymore with the corrupt ini file.
I tested with 1.4.1 and the daily build as of today, 2012-07-07. Both versions have the bug.