Very interesting read. Perhaps you can get to the bottom of why the protocol timing would often result in back/db lockups. I shot the AFD/AFD II/DF/DF+ and 645M, Aptus, P25+, P40+ and IQ160/IQ260 and all of them locked up at some point. XF and IQ3 series seem to have fixed almost all issues.
As a systems developer of communications protocols and definitive state machines that avoid/recover from such messaging errors I've always been of the opinion that the protocol or implementation was flawed based on timing assumptions vs robust messaging protocol. (My background was designing and implementing real time stock price & trading systems - things you can never lock up!)