[SOLVED] Sansa Fuze Plus original firmware pops up randomly

[il_mix]

Hi, everyone.

I'm using Rockbox on a Sansa Fuze Plus since the last month. Really satisfied with it!
I've had a couple of minor issues, but everything was fixed (I just needed to better understand the various RockBox functions).
A strange thing happened a while ago, and happened again a couple of times. When turning on the device, the original Sansa Fuze Plus firmware started. I was able to navigate and play music from it. Turn off and on, RockBox showed up again.
What happened?
Thought the original firmware was completely wiped out. Instead, it is still there.
Also, looks like the bootloader sometimes starts it instead of RockBox.

Any hints?

[wodz]

What about reading our fine manual? https://download.rockbox.org/daily/manual/rockbox-sansafuzeplus/rockbox-buildch3.html#x4-230003

[il_mix]

Shame on me... 
Is the second time that I missed a feature due to my laziness regarding reading documentations. Will be done, promised!
Thanks for your help.