Changing the C1 property of a weld causes Part1's hitbox to act strange

I was tweening the C1 property of a weld when I noticed something strange. Whenever I change the value of C1 by about 5 studs from where it was originally welded, the hitbox behaves bizarrely. You are no longer able to select the block and other blocks phase through it as if it was cancollide false.

I have created a roblox level where this can be replicated:
ChangingTheC1OfAWeld.rbxl (559.1 KB)

To replicate this, open the roblox level then hit “Run.” Now just wait 10 seconds and a script in the game will change the C1 properties of two welds. The Part1 of both of these welds will be the two black blocks in the game. Pick one and try to select it normally. The only way I was able to select the block was by dragging a selection box over it. Next, notice that the black box is cancollide true. Try inserting a block from the insert window and drop it on top of our black box. It should go right through it (oddly enough).