47: Re-Opening the Bet.
A: In no-limit and pot limit, an all-in wager (or cumulative multiple short all-ins) totaling less than a full bet or raise will not reopen betting for players who have already acted and are not facing at least a full bet or raise when the action returns to them. If multiple short all-ins re-open the betting, the minimum raise is always the last full valid bet or raise of the round (See also Rule 43).
From link provided by Vorpal. Bold fragment is exactly what we need.
Another example:
EP limps 2000, MP limps 2000 , CO raises all-in 2500.
BU, SB and BB can reraise freely because they didnt acted yet. Same with straddling players.
EP and MP can't reopen action because they acted already and after their action there was no valid raise. Obviously if lets say BU raises to 7000 then it lets EP and MP reopen action as they are facing valid raise(from CO).
Keep in mind that if we had something like EP limps 2000, MP limps 2000, CO raises all-in 2500, BU raises all-in 4000 then EP and MP can reopen action as BU all-in meets requirements of valid raise(minimal raise over last valid raise, so 2000, not 2500 from CO!).