attaching the silencer to the weathered 10mm pistol makes the gun disappear and the screen gets real bright. Also in third person there is this weird yellow aura surrounding the courier and a big red exclaimation mark floats in the air nearby. experimenting with this weapon mod always results in this.

the gun still works, indeed it seems to have become lethal with one or two shots even though its DPS hasn't changed. Also enemies behave as though you have "put your weapon away" so it must be invisible to them also.

there are other weapon mods which give unexpected results but loading and 'trying again' usually sets them strait. The most amusing one was putting the extended tube on the dinner bell which loaded all eighty shotgun slugs I had into it. I didn't like that so I loaded and mod my dinner bell again this time only eight shots in the tube. Much better.

I noticed the same thing. Kinda annoying