Why are absences being automatically withdrawn by the system?

We are receiving more frequent reports of absences being automatically withdrawn by the system. This is just one example from a supervisor:

My employee submits vacation time for approval. I receive an email to approve it, and in the same minute I get an email saying the request was withdrawn. The vacation time is still getting taken out of her total. Her last few timesheets that this has happened on say they are submitted and not approved, but I am approving them. This started when the email format was updated the end of November/beginning of December. My other employee is not having the same issue.