Checkpatch ignores spelling error by using -f

[Rolf Evers-Fischer]

Hello,
I've just checked the file drivers/tty/serial/8250/8250_omap.c, using 
checkpatch.pl, but I forgot the '-f' option (for file).

Surprisingly the checkpatch script reported a misspelling:

"WARNING: 'additionaly' may be misspelled - perhaps 'additionally'?
#417: 
         * We enable TRIG_GRANU for RX and TX and additionaly we set"

Additionally it reported that the file does not appear to be a 
unified-diff (due to my mistake).

Running checkpatch again with '-f', it didn't report any problems:

"drivers/tty/serial/8250/8250_omap.c has no obvious style problems and is 
ready for submission."

Is this a bug in checkpatch.pl? Or is it a feature?

Kind regards,
 Rolf