This is the problem I encountered starting out with the upload limit

In the "about:upload limits" it states that "If you have 15 slots or less, then you gain a slot for every 10 approved uploads.", which is correct, my upload limit went from 15 to 16 after 10 approved uploads.

Now, in the "about:upload limits" it also states "You lose a slot for every 3 deletions.", which is weird in my case since after the third deletion, instead of from 16 to 15, it went down from 16 to 14. After that another 3 deletion makes it went down from 14 to 13, which is correct (only 1 reduced upload limit after 3 deletions).

So the flow is like this: Starting out 15 upload limits -> got 10 approval -> 16 upload limits (right system behaviour) -> get 3 deletion -> 14 upload limits (wrong behaviour) -> get another 3 deletions -> 13 upload limits (right behaviour)

Is there a "hidden rule" I don't know of that made me lost 2 upload limit after 3 deletions or is this a bug in the system?