Parts disappear after undoing certain parenting actions.

[__Mine__ 1.9k]

When clicking Undo after parenting multiple parts in certain ways, one or more of the selected parts will disappear from the parts list.

To Reproduce:

1. Create three parts, all unparented. For simplicity, I'll name them "Part A", "Part B" and "Part C".
   
2. Select Part B and Part C, then parent them to Part A.
   
3. Press Ctrl+Z or click the Undo button to undo the previous action.
4. Part C will disappear.
   

It's worth noting that trying to add another new part and naming it "Part C" will give you a "Parts cannot have the same name" warning. Additionally, if you try saving and reloading the model, thinking it'll make the vanished part come back... it'll actually be permanently deleted.
And worse, if the part that disappeared happened to contain any shapes and/or additional parts, they will also be completely deleted along with the part itself when saving and reloading the model.

This obviously presents a pretty big problem, especially in models containing a lot of parts with complex shapes; worst-case scenario, this bug could potentially wipe out hours of work without the creator even knowing until they reload their model.

[ItsBluefindude 235]

Strange bug, I never experienced that, but it is a big problem for modellers, I do hope this bug gets fixed soon.

[Lock_downmc213 126]

Oh yeah this bug. I have experienced this bug multiple times and i can say that with certainty it sucks dongs. Not putting them into one file, I usually delete parts that are parented by accident and when i redo the part that i deleted disappears.

Edited June 7, 2021 by Lock_downmc213

[Fox Miner 3.6k]

I always had that bug when I forgot to save after big changes, and then it was all gone! I would recomend always saving and then it won't appear, at least I think so!

[FredMCGamer 649]

So that's why my rigs had missing parts!