I have found plenty of other forums but sifting through 20 some-odd pages of posts on the official forum I couldn't find a bug report of the following two bugs:

Quest: Oh My Papa
Issue: Melissa is missing from the Great Khan Encampment near Junction Cove (Deathclaw quarry).

Not only is it impossible to navigate around the area to search because the Deathclaws are impossible to kill without glitching them by standing on top of a rock, it is extremely disheartening that Melissa is missing. The only way that I've found through research is to complete Oh My Papa first and foremost, before Don't Make A Beggar of Me. On my first playthrough I didn't know this and can't complete the quest line so now I'm stuck with 3/4 Khan officers convinced.

Weapon: Weathered 10mm Pistol
Issue: Modding weapon causes screen distortion.

I couldn't say if it was a silencer or a scope, as I modded both onto it, but now I can't use the weapon at all because the screen goes practically all white and character is not holding the gun in its hand - there are no crosshairs, either. Fortunately there are more powerful guns, but I got the DLC when I purchased the game and was really looking forward to this weapon

The Weathered 10mm was supposed to be a UNIQUE weapon from one of the pre-orders. This may be a bug that is permitting you to mod the weapon, as all other UNIQUE weapons are un-modable.

I think I heard that if you cause a Deathclaw to run up the pass between the two Khan encampments, that it can actually kill her. Check for her body on the ground.

He's right, Melissa has disappeared. If he did her quest line before "Oh My Papa" then she has disappeared and he's stuck.

My husband add a clip mod to the weathered 10mm gun & now when he equips it, it has a large red ! mark. It still shoots. I thought you couldn't equip mods on speacial weapons. http://i3.photobucket.com/albums/y61/Nikki-chan18/Fallout%20New%20Vegas/2010_05210002.jpg