Thanks for all the replies :) I'm glad at least one has the same thing, might be we have the same mod/s, and that one is the culprit :D
It isn't a huge deal, just found it odd that they queue up to use the toilet while upgrading, when their bladder is fully green. Odd with the dishwasher too, because I've not seen any sim ever do any upgrading on their own. To queue one up when they are working on the object is just strange. And so far, I've only seen this with these two objects. I always upgrade everything practically in every house I play (and that's hundreds by now). Every sim of mine end up with maxed handiness. My sims don't inherit money, they inherit upgrade parts :D
ETA: Tested without mods, didn't happen. 50/50, didn't happen. All mods in, didn't happen. So I'm just as clueless as before :D will need to keep an eye on things.