There appears to be a bug. If 5 different recordings have been made, no matter how short they are, the next time you power on and try to record the error message will display (which you can't get rid of unless you press 5, AKA "exit"). If you go through the lengthy process of deleting a recording, you can then record again. But again, no matter how short that recording was, the next time you power on again and try to record you are greeted with the same error message.
Now, if when you get the error message you press 5 to "exit", and then you press record once again, it WILL record. And then you can record again after that recording without the error message...that is until you power off and power back on...then the error message comes back.
I tested this on multiple keyboards and the bugs are consistent. This keyboard is begging for a firmware update.
Regarding the inconsistency between black and white keys:
This might be more of a hardware issue, but when playing quietly, the black keys are much more quite than the white keys. This problem is very consistent. When playing loudly it's the opposite, the black keys are louder than the white keys. This makes playing musically and fluidly impossible.
