In my map, there are two AI's who start the game with 4 hatcheries (placed with 'create unit' trigger) and 12 drones (preplaced). The bug happens when 2 of their hatcheries are destroyed. Oddly, it has to be a specific two hatcheries as well. each computer's hatcheries are on either side of the map, two are in the middle with the other 2 north and south of them.
3 4
1 2
2 1
4 3
above are the location numbers for where each hatchery is created, the bug happens when both of the hatcheries at 3 and 4 are destroyed. hatcheries 3 and 4 are both on high ground while 1 and 2 are on middle ground, so possible the high terrain has something to do with it?
what happens is once hatcheries 3 and 4 are destroyed, the drones will all "stack" around the remaining hatcheries and stop mining. other than that they seem to continue building combat units as long as they have money and their supply isn't maxed, they don't seem to build overlords after this tho =/
if you think you can help and want to see the bug as it happens, the map can be downloaded here. right now all command centers are invincible until the end of the 20 minute timer for testing purposes, unless you want to see it happen later in the game i suggest you change that.
None.