Well, we got the plaster done and filled the pool. Noticed that an area adjacent to the pool was turning in to a mud pit but didn't pay much mind at first since we had gotten a bit of rain and we were still awaiting the final grading. Then noticed that the last foot or so was taken an awfully lot longer to fill than the first 8'. Then noticed that the mud pit was getting muddier and muddier. Then turned off the water and, by the next am, the pool was a good 6" lower than the night before.
PB has been good through all this...came out yesterday to inject dye into the inlets to see (I presume) if the leak was around the seals. Then plugged up the inlets to see if any additional drop. Is coming this am to see the results (and no, it doesn't seem to have dropped any more, so hopefully it's an external pipe, and one that's not under the concrete decking!)
Meanwhile, our plaster is curing away without the benefit of any chemicals or without parts of it being submerged. PB also recognizes this potential problem and has promised to stay on top of it and any problems that may come up down the road. Anything else that I should be aware of? Will keep you posted.