Playing through BGT-BG1 as a mage and doing a lot of spellcasting, seem to have bumped into the same thing soon enough.
I've noticed that a lot of times when game freezes, marker changes to "casting something on self", even though it never corresponds to what actually happens.
That, and a frequent (esp. in battles) "can not cast multiple instances of the same contingency spell on yourself" messages led me to issue, known as "Turumbar's contingency bug", which is annoying as it is (with these bogus marker feedbacks and messages), so I've disabled it as suggested in other (easily googleable) topics - by firing up NearInfinity and editing baldur.bcs and baldur25.bcs to comment out (they disappear after compiling/saving these scripts) lines with "TUDRWUD" in them.
One surprising effect seemed to be that I went through two areas now w/o a signle freeze, while it was insanely common before.
About the only other change I've made slightly before that today is disable party AI (untick icon in bottom-right corner of UI) - got tired of it, but I've got a few freezes after doing that and before commenting out contingency casts.
I'm not a modder myself by any stretch of imagination - please take this with a grain of salt, but as far as such gameplay issues go, it really makes the game much less playable, so I thought I'd share it nonetheless.
I'll try to edit this msg out of existence if I'll get similar freezes again.