PerJobCredentialStore is kept in ExportTable and is never released which can leads to OOM, for details see [1] and also [2].
[1]http://jenkins.361315.n4.nabble.com/jenkins-running-out-of-memory-heapspace-I-have-a-memory-leak-td3658830.html
[2]http://jenkins.361315.n4.nabble.com/Severe-memory-leak-in-hudson-td3162254.html