Not sure if this should be considered a bug just because it doesn't behave the same way $replace() does.

If /breplace is given an odd count of numbers greater than 2, it doesn't report the same error as when /breplace is given just 1 number.

i.e. error vs no-error for 5 replacement tokens:

Code:
//echo -a $replace(string,a,b,c,d,e)
vs
//bset &a 1 13 10 13 10 99 | breplace &a 10 13 13 10 99 | echo -a $bvar(&a,1-)