Ah!! a new one.. It may be a burr of the sear/hammer interface or some of the wonderful preservative grease they put on those things.. Can you strip the weapon? If so give it a good cleaning and check the sear/hammer to verify they are meshing.. If you do more than clean it you take the chance of voiding the warrantee.. So your best bet may be to return it if there is a problem found.. Perhaps the dealer you bought the shotgun from can fix the problem.. Most have some gunsmith backup or he may elect to return it to the importer. As an aside you can run a little test for yourself. after making absolutely sure the weapon is empty(read unloaded) cock the hammer by hand and push on the rear of the hammer spur. It should not push off.. If it does it is very likely the sear/hammer surfaces are the problem..
PS- just a thought but on these old guns the trigger is in a seperate group and the sear/hammer ride on the rear of the carrier group. If anything impeeds the return of the trigger of the disconnector the gun may follow or fail to function correctly. The shotgun was designed to fire as the weapon's bolt locked if the trigger were held to the rear. This was a common feature of older shotgun designs. It makes for a very quick firing weapon indeed.
