holding down control-B gives a stack overflow
control-B interrupts the running process with a BREAK. if you type a control-B while the break window is opening, it will interrupt the creation fo the break window. Just holding down control-B will ... etc.
Control-B interrupts should be turned off, but carefully.
control-B is an interrupt character ... the function LISPINTERRUPTS returns a list of initial assignments
I think perhaps this should be "won't fix; operating as intended" - don't hold down/repeatedly type ctrl-B ?
if you have a bug in scroll handler you also can wind up with lots of nested break windows. I think it's reasonable to turn off the keystroke that caused an interrupt until a safe state (I'm not sure when that is -- the prompt in a beak window?
I marked this as 'low priority' but as we get into the keyboard handler and key assignment rationalization, it's another thing to keep in mind.