My group and I have only played a few missions in the beta, but a lot of my team mates were complaining that their character would stop and switch weapons whenever they got shot. This would often lead to them getting shot a second time and dying from it, as their character would stand still to bring out their sidearm.
EDIT: This has not occurred since .72 went live.
I tried really hard to reproduce this on cue, but honestly I couldn't. I did, however, finally get the problem myself after I started using a weapon that my character did not begin with. I took a weapon from a crate and then every time I got shot, I switched to my sidearm.
I was using a revive script, called =BTC= Revive, version .91 when all of this occurred. The script designer came out with a new version, so I will test to see if the script was some how responsible, as we were using version .90 until beta when this started happening.
I don't believe this is actually fixed. Was playing with a bunch of friends last night and it kept happening, but in my case, it kept pulling out my AA launcher. There was no rhyme or reason when/why it happened, but it was happening times I either got shot or took damage (explosions, etc).