As much as 3 or 4 years ago this was already going on. I had only ever purchased one bomb vendor... and it randomly duplicated. I reported it. Ignored the issue.
Since then, there's been tons of things that have just randomly popped up in my inventory, including but not limited to swimming pools, slides, and (most expensive) a key block.
I've reported it every time. No one took the time to make any change... and the important part is even though there's a timer on the placement/deletion of objects now, it still happens from time to time.
The timer is not a solution, any more than shrugging your shoulders and nerfing resale prices is.