Pull requests are associated with incorrect issues after destination is changed

Steps to reproduce:

1. create a pull request with source from branch A and destination to branch B (suppose the commits to be merged contain issue key ABC-123)
2. synchronize the repository so that the commits to be merged are recorded and the PR is associated with issue ABC-123 on the Development panel
3. update the pull request to change destination to branch C, so that the commits with issue key ABC-123 are no longer in the list to be merged
4. synchronize the repository
5. result
   • expected: the PR is disassociated with the issue ABC-123.
   • actual: the PR is still associated with the issue ABC-123.

Workaround: Do a full synchronization on the affected repository from the "DVCS Accounts" page.