USB flash drive not seen on USBOTG port

Hi! I used to be able to plug my USB flash drive on my FP1. Yesterday, I switched to a FP2, Open Source OS. I cannot just plug my USB flash drive anymore.

The USB port and adapter cable work, since:
— I can plug my Logitech wireless USB mouse, and it works ;
— I can su in a terminal, and mount -t vfat /dev/block/sda1 /storage/usbotg and Amaze shows me the files (although with a wrong encoding of latin characters), however I cannot umount after that…

Now I wish:
— that OpenSource FP Android would see my flash drive on USB OTG without the help of a su command,
— and that I could disconnect my flash drive afterwards.

Where is this “hidden feature”?

(My feeling so far, is that Android 5 is a big step backward from Android 4.2.2…)

Before the 1.2.8 update it worked well on the FP2, so I think it’s not a general Android 5.1 “feature”, but a new bug that was caused by the update. And since the FPOOS is based on the same updated OS version, I still suggest that you follow this thread to find a solution.