I believe -iexten may be the problem. In your tty1 test, was iexten enabled?
Maybe a getty bug, it should be turning on iexten if it turns on iuclc.
I was able to recreate the original problem. Reading Alan's response
here I was surprised to see that adding iexten to iuclc did enable the
desired behavior. This would not have been required on traditional
systems and its combination here isn't obvious to me. There doesn't
seem to be very much documentation available about iexten. I am
curious how you deduced that adding it would produce the desired
behavior?