I have noticed on several friends 22AR's the dust cover just will not stay shut. It seems as though the little detent pin is just a shade to short. Anybody else notice this or am I just seeing things?

The ejector port cover is not intended to function on the Colt/Umarex M4 ... and mine didn't. There's a cut-out on the upper that prevents the cover from clasping shut.

I've since replaced my "dust cover" and found that the replacement had a larger (fatter) pin and it will close, however, it will only close if the bolt is pulled back on an empty mag or upon inserting a fresh mag. It will not close if the bolt is closed, which is fine with me.

My port function , I have no problems...Is strange.