Whoa, that sounds well known... from an ancient version of PODBot mm. Does it really occur with the latest build (r2b46), too? I really can't imagine. The other day I was waypointing a map where there is some shootable ice the bots can walk on. And although there was no connection leading through the breakable ice, bots stopped, shot the ice at their feet to pieces and drowned...
sPlOrYgOn has messed around
a lot with the code that makes bots shoot breakables, and the only thing I could imagine is that part of this code might not work correctly while bots are stuck to ladders. But first please check if you are really using the latest build of the bot dll.