On the 6th of June, I received a reply from Ectaco regarding this issue saying:
"There were a few issues regarding flicker in Jetbook, but it’s been fixed by new Firmware version, so there should not be any problems."
I just wanted to check if this is still an issue (don't reply if you do not have the latest firmware).
If it is not an issue anymore then at least the next person reading this post will know that the problem is solved. Therefore I will not apologize for the bump of this old thread.