krcollins:It is absolutely not absurd to think that someone would remove a second stage for a variety of reasons such as swaping out a hose. The OP says he didn't and we should give him the benefit of the doubt but it certainly is not outside the realm of possiblities and way far from "absurd".
No what's absurd is that he would have done this and then refused the shop's offer to service the reg for free.
krcollins:The important thing is that we will all think about including this in our pre-dive checks.
Amen to that. I'm picking up my reg from service this weekend. Between this post and the note in the last issue of Undercurrents about a woman who died on her first post-service dive when her reg failed at depth due to an improperly installed diaphragm, you bet it's getting more than the usual couple of breath while watching the SPG test.