No, it is a plain setup issue. Build your own kernel either witout ddb or with the console magic changed. You can create a "GENERIC64.local" file with no options DDB or if you want to keep ddb but disable the serial break to enter it options CNMAGIC="+++++" and all will be fine.
I think you mean GENERIC.local, since the BBB is only 32 bit.There are two issues here: one is that removing the serial cable while the machine is running can cause the kernel to drop to the DDB prompt, which can be fixed with above, and the second issue, which the first might inform, which is that with no serial connection at all, the machine doesn't boot unattended.
If it does boot unattended with the above, then I'd wonder if initialization of the console causes something that the kernel then perceives to be break-like.
John