This sounds like exactly the same bug that plagued Fallout 3 after its release on PC and 360. I think it was down to missing data or something. There are videos of it on YouTube.
So not only does New Vegas have its own bugs, but it seems to have re-introduced some which were eliminated in Fallout 3. It would be funny if it weren't so pathetic.
When I used the G.E.C.K. for Fallout 3 on PC, the big red Exclamation Point would appear if there was a file being used that wasn't connected to a skin or some other form of data.
Basically, that combination of weapon et al. into the new silenced pistol probably wasn't skinned by the Devs and the big Exclamation Point is a reminder to them (or the person using the editor) that they need to skin it before shipping it. Unfortunately, they shipped before they skinned.
Skinning > Shipping