Disabling mailing groups causes emails sent to that group to disappear from scheduled and sent mailings

When a group is disabled any mailing that used that group disappears from the scheduled and sent mailings. The mailings reappear when the group is enabled.

I first discovered the issue in 4.1.5 and recreated it in 4.2.7. I'm sure it affects more than just these two versions, but have only confirmed it as a problem in these two.

Also, disabling seems to cause different behavior than deleting the group: after I deleted the group in the demo the mailing still appeared under sent and scheduled mailings but when I disabled the group it disappeared.