Limiter burst doesn't have any effect
No matter what you put in the burst field, the limiter behaves exactly the same as if it's 0 or null. Re-tested on the most recent 2.2 snapshot as of now, and it behaves the same in every 2.1.x stable release. For example the attached traffic graph, that's 4 Mb down (out), 2 Mb up (in) limiters. First run with no burst, second run with 400000 thrown in as the burst. Doesn't matter if that's a small number or huge number, it has no effect at all.
I'd be fine with just removing the burst field for 2.2 if fixing this is really involved.