Ah i figured it out now too. Pircbot will not update the isOp for me so i overwrote the onUserMode(String, String, String, String mode) method (standard implementation does nothing) and made it add/remove the user to/from a Set. This solution worked for me finally.
Btw: the String mode of onUserMode(…) contains following: “#Channel +o user” (or -o if moderator status was removed)