Tried something out just now as I am on that same scenario and trying to work out the best starting process to do ...
But I set a mechanic to only handle vandalisms and he ran off and fixed a bench .... then started idling and didn't fix the bench next to the one he just fixed.
So far, from game play I have noticed the following priority system for the mechanics ( assuming all items ticked ).
Repair Habitat Barriers
Repair Facilities
Repair Power Facilities
Repair Water Facilities
... Other stuff not identified yet
Will use the scenario to set up a work group with just one of each type of repairable item and see which order he does it in.
So, it looks like the vandalism element is bugged somewhere if it works once, but will check that again as well