We tried it without any modification...
The problem appears to be that the advanced Search does not recognize #.
In a search for PI#233849, it also searches for PI
BTW, we have Display Keywords turned off, but turned it on briefly, and noticed that with thumb titles having PI#233849, that the keyword showed as PI 233849. The # character was not in the keyword.
Also, as mentioned previously, the search box on index page DOES WORK.
Typing in PI#233849 does indeed find these pics.
Hope this helps find the problem,
Mark and Carole