I recently processed a wafer and mistakenly used the wrong mask at a
certain step.  After removing the photoresist, I noticed that the areas
which had been developed were hydrophillic and the areas which had been
covered with resist were hydrophobic.  I don't know how long the effect
lasts, but I dipped the wafer in water and dried it about 5 times and the
effect remained.
Conditions were AZ 351 developer and AZ positive resist on GaAs (with some
epitaxial stuff on top).

Marty