I've had a few fuse explosions that were the result of one set of poles connecting to another - always large power poles (my backbone in my current save) connecting to medium, when those large power poles were placed by robots.

I think it only happens when placed via a blueprint or via ctrl-c/v (which I think internally uses a transient blueprint). It doesn't happen when I place a ghost.
That said, I've tried to repro before and it hasn't repro'd, so it may be game state as well.

Sorry to leave an ambiguous report. Happy to provide any more info if it'll help you.

Yeah, poles placed as a result of blueprints get automatically connected, which can cause problems like this. If I cut the connections, then blueprints of things like pole -> fuse -> transformer get completely broken. Sadly the 1.1.x API doesn't really have enough for me to fix this problem, but in 1.2 I can deal with the connections of the ghosts directly, which should help.