in some constellations of piston/redstoneblock there are some bugs.
Constuction as in the fist picture:
when I switch the lever the piston extends and so does the upper one because of the redstone block.
but when I switch the lever again the piston remains extended.

Construction as in the second picture:
when I switch the lever the upper piston extends and so does the upper one because of the redstone block.
but when I switch the lever again the lower piston pulls in and immediately extends again.