If you look at Bojidar's K-mount page
Features and Operation of the Ka Mount
you can see that the pin that is missing on the 1.5x converter is the so called "m2" pin.
Your A400/5.6 is an f5.6-f45 lens.
This would mean that the pin m2 should be isolated (
011*00)
(Compare the table on the page linked above.)
Since the pin m2 is not present, it will be conductive always, giving a
011*10 lens, which is, according to the table, an f2.8 lens.
I have no idea why Kenko built the converter in such a strange way.