Yeah, it has happened to me as well, quite a bit of times actually, but I never had more than 5 men die during a single battle from this pathfinding bug. This always happens during wall battles and it has happened to my men even when they were just moving. Every time this has happened to my units while they were not fighting was when there were two much men on the same stretch of a wall. Jams happened and the next thing you know, people are falling. The Arabian slingers aren't jam-packed though. Odd.

It could be connected to the undermined portion of a wall right by those slingers. I remember sapping a wall, killing a bunch of AS phalangites who happened to be standing right in the same place the undermining was done, and then a two minutes later, a couple of them fell from the wall for seemingly no reason. They weren't moving either.