In the editor mode, whenever i have a block or part selected and i click on the interface to select a new tool or part while the interface is overlaying the construction perimiter, the game places whatever i have selected.
When i select a new block it places that block roughly in the place the option is in the menue. When i select a tool it places my last selected block in a seemingly random position. I think the problem is that wen you interract with the overlay menue, it still interracts with the construction area. When the menue is not over the construction zone this bug does not happen as it is an invalid block placement.

When your mouse cursor is on the menue it should not be interracting with the game world.

I hope this explenation was sufficient.