This is almost certainly linked to
this bug, in which case it should be fixed for the next release.
Nope, i have testit it with both settings (file extensions on and off) both load the script file as it should be.
I also registered the filetype .mrc to a custom app to hide the extension, it's not related to that bug.
Tested on Win7 x86 Prof. with mIRC 7.14
And about HaleyJs problem
I can't confirm or reproduce it on Win7 or XP