I've been pulling map packs from the below link and installing them. I haven't had any game stability trouble installing individual maps one at a time manually, just with the map pack installs.
http://www.battlezone.furion-gaming.com/mappack.html
I've put 3 on and have had varying amounts of trouble with them. Right now, I don't have any map packs installed in 1.5 as I've seen a general increase in lockups. The ones that are definitely causing me problems are:
BZF mappack 2 - lockups
Katz mappack 3 - Katz hacked the install to show that goofy icon of his every time you change a screen in the game... very annoying (I always knew there was a reason I didn't like that guy!). This map pack also seems to affect game stability (periodically dumps out of the game completely and into Windows with pack installed).
BZF 1 mappack: seems OK mostly - but a couple lockups (game freezes) with it installed.
I've gone to just manual map installations. I've only installed DM maps so far (about 10-12) with no stability problems. I wasn't able to run mapadder on my 64 bit Win 7 machine, so I've just been doing the installs manually.
I can't point to any specific maps as a problem as all my manual adds so far have been OK. There's something buried in at least some of the map packs that is causing a problem. I'll update this as I run into more problems. I may have another go at the map packs but I'll save complete copies of the 1.5 files before I do this again.
FYI: The following maps seem to run OK, but don't display map overview pics when selected in the launch screen:
battlefld (DM)
Drive In (DM)
High Road (ST)