Strange property of ManualWelds?

I have a script that creates ManualWelds between part A and part B. One of the welds has Part0 as A and the other has Part0 as B. After a brief moment, only one ManualWeld remains. What’s up with that?

Maybe ROBLOX commissions monkeys to perform secret optimizations behind the scenes?

Because what need would there be for multiple ManualWeld instances connecting the same two BasePart instances?