A fix with a format change would be to put the padding byte in front
of the sub-page instead of at the end.
Ignore next paragraph:
One fix with a format change could be that the data item gets uneven
size too, with a padding byte in front of the sub-page.
Because that's repeated as the 2nd alternative after this one:
The most general way would be to do that in all nodes with uneven-
sized key and even-sized data: