We just had a 24 x 13 popcorn ceiling torn down and sheetrocked. While it
was down, I had my plumber install new waste and toilet lines in the Master
and Main baths because the plumbing inside this ceiling had evidence of past
leaking and most pipes were of corroded galvanized. Of special note is that
the drain for the main bath shower was dripping....at least we think it was
the drain because the water was dripping from that vicinity (read on)...

We called our plumber to look and he said he ran the main bath tub and no
leaking occurred where noted. He also noted that this particular bathroom
had all new waste lines made of copper, unlike all the other waste lines
made of galvanized and in need of repair. However, we still insisted it
leaked because I had a bucket under there and saw the drips.

He replaced all the waste lines with PVC and the new ceiling went
up...spackled, painted....the whole bit. We've taken a shower for weeks
after this....no problem. Suddenly, several weeks after the plumbing job and
for one week straight now, we are getting small amounts of water (about a
half or so full of a dixie cup) coming through the recessed light where that
shower is located above.

The mystery:
1. I test run the shower with the tub closed and no leak
2. I test run the shower with the tub open and no leak
3. I test run the tub faucet with the tub closed and no leak
4. I test run the tub faucet with the tub open and no leak
5. I switch the diverter and hot/cold levers back and forth and no leak
6. I run the sink faucet and no leak
7. I flush the toilet and no leak
8. My wife takes a shower and no leak
9. I take a shower (usually after her) and it leaks!

I thought it might be my weight, but my wife is pregnant and now weighs the
same as me!

This pattern is consistent and neither I or the plumber have a clue or a
solution. He said he'll take the ceiling out and have a look, but I'm really
trying to avoid this. Do you have any suggestions of how to troubleshoot
this further before I have to rip apart the ceiling?