Well, considering how specific this problem is, how helpful you were with the info requested to reproduce the bug, my free time tonight and how trivial would be to make a tiny fix, here's... well, a fix.
This file will restore the old behavior (firing both weapons when you press fire once), therefore avoiding the dissapearing double RL animation; however, you must run at the end of the command line, because if you load it before aeoddat.pk3, it wont work.
You'll see a warning message in the console, but that's inevitable.
Edit: note that this isnt an official patch or anything. Is merely a simple instafix for you. People shouldnt use this unless they experience the same issue.