Ah, hier steht etwas dazu:

PARM (Parameter) statement

*CMDSTR: The parameter value is a command string that is checked for validity by the command analyzer. It is passed to the CPP as a character string.

The command analyzer rebuilds the command string when it checks it for validity. When the command is rebuilt, keywords are added to parameters that were specified positionally, parameters can be reordered, and parameters that contain characters that cannot be printed (X'FF' and X'00 - X'3F') are converted to hexadecimal notation. As a result, the rebuilt command string may be substantially longer than the original command string. If the length of the rebuilt command is longer than the allowed length specified with the LEN keyword, the command will fail.