Sticking to ladders sometimes

Try talking to an NPC with multiple dialogue options; See if it continuously goes up. Though it sounds like you may have tested this already.

Finally had it happen again (it's intermittent on my 2nd desktop which I don't play on much) - talking to an NPC doesn't fix it.

When I talk to an NPC, it stops, even after the dialog is closed - until I click somewhere on the screen - then it starts climbing the rope again. Kinda weird.