I had this happen to a mule that was lvl 1. A handful of lvl 50 weapons were converted to random levels when I fetched them. Not sure if this goes both ways though.
I think this only happens with mules that you got to sanctuary without actually playing to get there. i.e. Creating characters in a buddies hosted game, and claiming items there. Happened to me with lost loot machine when trying to expand their storage. The ones I got to Sanctuary through the quest-line have not had this issue.
yeh but still a nasty surprise