Just got a reply from the support, concerning wrong tags and other questions.
"We will continue to look into the tag problem. Thanks for the information you provided.
If everything goes well, the X5's next firmware will support folder jump function. By using this function, you can play a whole folder when go to browse files.
Regarding to the random play, it exists some algorithm problem. The new firmware will solve this problem, pls don't worry. At present, we can't confirm the exact release date of the X5's next firmware."
So, basically in the new firmware tags will be unnecessary, given folder jump and playing folders with subfolders, and random will be random, the problem is acknowledged. Good!