Throttle exceeds limit after a delay

[StructByLightning]

I'm making API calls to a rate-limited endpoint (1000 requests/minute). I set p-throttle to allow 900 requests/limit and for a few minutes it seems to work fine. But after that the rate spikes to about 1100/minute, and shortly afterwards we get 429s from the API for exceeding their limit. I'm not sure why this happens. We're using the strict mode mentioned in #26.

I can provide a demo if necessary.

[sindresorhus]

It would be useful if you would be able to provide a failing test.