Here is what the behavior will look like.
Update: Microsoft has released an update (KB2803821) that should resolve this issue for Windows 7 users.
Update: This issue has been resolved in version 8.1.2 for single WMV files. For any .camrec files with the problem follow the steps below.
This issue is caused by a specific Windows Security update. It affects more than just Camtasia Studio. Uninstalling the Windows update can be used as a workaround to the issue.
Windows 7 update: KB2803821
Windows XP update: KB2834904
To do so click on Control Panel > Programs and features > Installed Updates
If you don't see it in the list try searching for it as shown here.