This issue is a little confusing. So, if you are not able to reproduce let me know i will send you a video to help reproduce the issue.
Reproduction Steps : 1) Let's say you are User A who is inviting a user B to abug report, User A goes to + sign(adding participants) and adds a email address there. 2) User B gets an email immediately about an invitation, he accepts it and sees the bug report. 3) User A after few minutes of sending invitations realizes he made a mistake in email, and cancels the invitation which is still showing pending in his side. 4) User A is shown a message " The invitation to UserB has been successfully rejected.", he thinks now the User B is not able to see the bug report anymore. But to his expectation, User B can still see the bug report.
So what is happening? When User A clicked on the cancel sign to invitation that showed "pending", the cancel signed only made the invitation send to email invalid. But since user B has already accepted the invitation, User A's clicking on him won't remove User B from the bug report.
So what should have actually happened? When User A clicked on cancel sign to invitation that was showing "pending", it should check if the user B has already join the bug report or not. And if User B hasn't it should make invitation code invalid, and if User B has already accepted and joined the Bug report, it should revoke the User B's access from Bug report.
I hope this clear enough to understand.