Just to clarify...
1) Is the actual pin in the receiver loose? IE, you grab just the pin between your index finger and thumb and you can feel it move?
OR
2) As the others surmised your speaking only loose when the barrel is opened.
If #1 this one IS A PROBLEM.
If #2, as Spanky and Larry mentioned, its not and OK and likely will cause no issues.
Its fixed as Spanky outlined. I have had one very bad one that I made a shim from steel shim stock, that I fit behind the plastic spacer and on top of the wood.
CW