I am sure this has been mentioned before somewhere in the forum, but i thought i would bring additional information about it to everyone's attention again in better detail.
If you have any companion(s) with you, they have weapons of any type in their inventory and they enter any casino on the strip with you, once your companion(s) exit, those weapons will be gone. (yes, we all know this)
I have read about this on in the forums here, but i thought making the companion wait outside in the strip or at the north gate or even in a totally different area would solve the glitch, obviously it did not as it still happens.
The only way is to remove the weapon(s) from their inventory or dismiss them either to the Lucky 38 or their shacks (if they have not been upgraded from a quest).
Also, if any companion has been upgraded from a quest, they lose those upgrades after exiting the casino as well, so removing the weapon(s) from their inventory wont matter at all.
Best suggestion: Dismiss them to the Lucky 38 before you enter any casino.
I found this out 4 hours after the fact when i realized ED-E's weight decreased from 5 to 1 (lost the upgrades from a quest) and Raul's full maintenance perk was working like the regular maintenance perk (weapons were degrading slowly).
Perhaps the additional info i posted here will help (if it already hasn't been posted), but i will say that besides the bugs, glitches, freezing and frame rate issues this game suffers from (on the PS3), that this is the most annoying glitch in the whole game, especially if you are not aware of it.
Thank you to the original poster who helped all of us become aware of it.