Try this:
1. Open a file F1 with extension .pm, Perl mode is correctly active.
2. Open a second file F2 with extension .pm, Perl mode is correctly active.
3. Change F2's mode to C mode.
4. Switch back to F1's tab and you'll see it's now in C mode!
Is that a bug?
-- fxn
Just in case you are wondering where does this convoluted experiment comes from: I am working in a Perl module that has some part written in C:
http://search.cpan.org/~fxn/Algorithm-Combinatorics/
There's a file ending in .pm that is strictly a Perl module, but that actually is mostly C except for a few lines, since it uses Inline::C. I need C mode there to work normally.