Knowing about tab does help a lot in the mean time, so thank you for mentioning it here, cause I missed that.
I just found I seem to be able to reproduce the bug pretty reliably by: add part > begin dragging it to new location > right-click to remove while still dragging. Also just found it leaves behind muscles that were attached to some parts as well.
Undo would be saver on the wrist so thank you for bumping up the priority on that.
Thank you for taking the time to read and respond it's appreciated!