I send a message to my entire list of course participants. When I try and send another message later to just a few of the participants, I select them and proceed but the messaging page still shows me the entire list of participants

Replication steps:

1. You have a course with participants.
2. Click the participants link in Navigation > CourseXXX > Participants
3. Select all and send them a message.
4. Now return to course and repeat process but this time you only want to select a few users to send message to.

Expected result: Only the selected users should appear on the message page.

Actual result: The message course users page still shows all original participants and they need to be removed 1 by 1.