Cross site state transfer - status of push gets stuck at "SENDING" after being cancelled

After invoking: site --cancelpush backupSite on the producer site, status of the push operation seems to get stuck at "SENDING" value (tested by site --pushstatus), even if state transfer is not currently in progress.
Invoking site --cancelreceive mainSite on the consumer site works correctly. New invocation of site --push backupsite leads to "X-Site state transfer to '%s' already started!" being displayed. The issue seems to be caused by XSiteStateTransferManagerImpl.siteCollector not being cleared.

Used configuration:
distributed caches, site A: 2 nodes, site B: 3 nodes, B is a backup for A.

Scenario

• Start A,B
• Take B offline using takeSiteOffline
• Load data into A
• Push state into B
• CancelPushState B
  • PushStateStatus remains stuck at SENDING & new push is not possible