Winbox not responding..
Took 20 attempts to connect using SSH..
Tried to do a reboot and this is what I got from SSH...

Reinstall with NetInstall, (clean the config). Update the bootloader(firmware) and try again. Use latest RouterOS (5.21 at this time).

Good luck!

There is an issue though. I have 4 750UP doing this. and 2 were NetINSTALLED after I noticed it around last month... Seems in the RESOURCES it starts showing less and less available memory, and then eventually lockup.
only thing thats running is HOTSPOT with about 20 users. My 450 's are not doing this

if you're sure it is a bug - take it to support (send them an e-mail with the supout.irf file)