You are correct. It doesn't work for me neither.
You can Copy & Pas... NO! That also won't work...
It could be that Minix U22-XJ is coming closer to becoming just an "entertainment device" after all.
Jokes aside, the chance to go around the Gmail App issue is to edit the draft in gmail inside a web browser. The incompatibility of some apps with the devices is something we probably always have to live with. It is an annoyance, of course, and I personally consider of high value that these subjects get pointed out as they will help to trace real questions that might hopefully trigger solutions.
Especially because I do believe pure Android devices have a way to go competing with other OS for productivity tasks.
Unfortunately I have no further solution for these Gmail issues for the moment. Maybe someone else will.