freeze plug problem

I just had my short block rebuilt by a local shop. Well I noticed that there is a old freeze plug still inside the block.

Is this a problem? or can I just put the motor together with no worries.

John

EDIT: I removed 4 plugs, the 2 rear plugs and 2 inside the motor!

as long as its sealed and not leaking its probley fine,my question is why would the shop reuse one of the old ones,are all the other plugs new,but if it where me I would replace it just for peace of mind good luck with the engine I got one i'm building up right now

what do you mean still inside the block? like an old plug still being used, or a freeze plug fallen literally inside the block?