I only found one const that included 450 in the driver-avalon.h. Thanks Tursk.
What do you think?
As I've mentioned, the easy way around this for now is to use the API to set the frequency at least once and it will tell you the correct timeout.
e.g. on mine just now:
java API "ascset|0,help"
Output: [Msg] => ASC 0 set help: freq: range 256-450 millivolts: range 1000-1310
java API "ascset|0,freq,400"
Screen: [2013-08-15 10:27:05] BTB0: Set frequency to 400, timeout 31
(I guess I better get around to adding 'd' as a timeout option now ...)
I've no idea what it would do to the chip to clock it above 450, but yeah, the timeout could be the problem you are seeing.