I also tested now with other adaptors and have the same problem again.
my testform has the label with the strange behavior, an enabled textbox and a commandbutton with the following code in the clickevent:
thisform.lockscreen=.t.
thisform.refresh
thisform.lockscreen=.F.
after several clicks, the caption of the label looks like faded out. When I remove the textbox the effect does not take place. Seems to me like a bug!