the solubilization of (polymerized!) actin dependes largely on the
detergents present in your lysis buffer. As long there is no SDS
present, I'd expect actin in the pellet.
I am deducting this from the fact that one may use buffers with eg
Triton X100 or Tween 20 to nicely dissolve adherent cells but keep
nuclei and the cytoskeleton attached to the well. You might easily
compare your lysis buffer with a lysate obtained directly by
sonication of your sample in 1x Laemmli buffer.