Re-election of a primary can be delayed because of a veto from another member of the replica set.
This issue can manifest if a replica set election is triggered and a member has not seen that the (old) primary has already stepped down. This will occur most frequently when there is a replica set reconfiguration event combined with either network latency or a node is overloaded. This fix shortens the time it takes to re-elect the primary; it would eventually get elected when the stepdown state is processed and it stops vetoing.
It is present in all versions of MongoDB prior to and including v2.4.6.
Don't veto former primary from re-electing itself.
Production release v2.4.7 contains the fix for this issue, and production release v2.6.0 will contain the fix as well.