After the last update, the behavior for duplicating parts (ctrl+D) changed.
When you select an unanchored part and hit Ctrl+D, the part is duplicated as normal but its physics start being simulated for a while, then they “rewind back”, sometimes incorrectly.
.gif:
To reproduce, simply duplicate any part using Ctrl+D (make sure the part is unanchored). It happens more often on Team Create.
Bonus:
Unanchoring models sometimes yields the same results (it’s not running):
