I use an Eclipse CDT bundle on which I have added PDT features, and
sometimes after loading up Eclipse, perspectives are resetted to their
default (meaning, there's no "PHP perspective" button, and opened
views/tabs are those available by default, positionned to their defaults).
I tried two or three times to reinstall from scratch, it changes nothing.
I don't know if this is relative to PDT project.
Note that i have 2 projects in my workspace who contain the same
filesystem folder. I know this is risky but... anyway, i always close one
project to use the other so i have only one opened at a time, and i
answered "No" when i have been asked if references should be searched in
other projects.