It’s the revenge of PHP debugging: for some reason breakpoints just stopped working on my Eclipse PHP IDE. This is apparently a known issue, even on release 1.0 of PDT.
After much hair-pulling, I’ve figured out a workaround: while debugging only stops on a breakpoint the first time while using the integrated Eclipse browser, it does work when configured to use Firefox as an external browser (Camino gave me an error on launch). To change that option, go to Window | Web browser and select something different from Internal Web Browser.
Hope it helps those out there still looking for a solution.