omj: i see, thanks for replying - I'll just live with it for now, as I've caved and ordered a Tilt 2 anyway (mainly so I can use the same phone in Canada and the U.K.) I don't honestly have enough data to say for sure it's when it's in locked mode that it won't pick up the call, but that's how it feels. The 'slide to answer' slider reacts and slides across to the side, then the screen just sits there showing the slider in fully-slid position for a while, then goes back to the home screen (not the lock screen...) showing a missed call. A bit strange. Ah, well. I'll let you know if I figure it out.
I had an overnight hang today as well :/ meant I missed my morning alarm, d'oh...
edit: I'm gonna try disabling 'unlock on call'. Maybe that has something to do with it. I can't remember what the defaults for Manila Locker are, though
edit 2: just tried calling myself from the house phone a few times. Changing 'unlock on call' didn't help. And from that testing, it's not the lock screen, it's just random - a couple of times it did work to pick up the call, a couple of times it didn't. Whether the phone was locked made no difference. sigh.