The PCOMP command in the 6000 language cannot be used inside of conditional statements. This includes Loops, IF and WHILE-UNTIL statements. It does NOT include REPEAT statements.
One ramification of this is that this includes using the PCOMP command after a GOSUB or GOTO command from one of these conditional statements. Neither the GOSUB nor the GOTO commands clear the internal pointers that link back to conditional statements. A JUMP command does. Therefore, using a JUMP command from within a Loop, IF, or WHILE statement works with a PCOMP command.