Originally Posted by kiwidude
I've confirmed the issue and you are dead right, the chm input reader plugin is not releasing a file handle. I'll add a report to the bug tracker, I've isolated it down enough to prove a fix that "works" but Kovid or someone will need to put it in the right place. So it will require a Calibre release to get the plugin to allow you to open CHM files without restarts.
Fine, i will wait for the next Calibre release