No it won't reset back to version C.
I'm not an expert on this, but I envision the firmware as a writable part of what would be the "BIOS" on a PC. I'm not sure if the Linux kernel resides in firmware, or partly so, or not at all.
In any case, when you flash your firmware, its what you got.
The only thing I didn't try when going up to E from D, was doing a reset on E. Knowing now what would have transpired... I would do that, since the reset was inevitable when retrograding firmware.
See if that fixes it up - the reset that is. Heck, if it does, I might just upgrade back to E and F.