Okay, got it now.
There is the "two panel mode" missing (on the right side).
Curious if others are seeing this? Seems strange it that happens on three different devices with varying hardware characteristics but all share a common ancestry (Amazon tablets running CM).
It's the size. I suppose that AquaMail considers that a tablet is a device wider than 8 inches.
AFAIK it depends not only on the orientation (portrait vs. landscape) but also on the screen size based on the
available screen width. Android divides the range of actual screen sizes and densities into a set of four generalized sizes:
small (), normal(), large() and xlarge ()
and additionally in a set of six generalized densities:
ldpi (low) ~120dpi
mdpi (medium) ~160dpi
hdpi (high) ~240dpi
xhdpi (extra-high) ~320dpi
xxhdpi (extra-extra-high) ~480dpi
xxxhdpi (extra-extra-extra-high) ~640dpi
-> see attached illustration / overview
As a result it is possible that Android couldn't recognize the screen orientation correctly.