It takes a long time to fill up vendor inventory, but I was able to recreate this bug.
Others have reported the same thing prior
Pic is of the statue falling at the same time as being paid a 10 piece Oinc
Steps to Reproduce
Build The Sty' Oddities Emporium. Sell multiple items to vendor; eventually inventory fills and he cannot hold any more. Gives Money, Item falls. Repeat for unlimited Oincs
This issue has not been confirmed by a developer yet.