Can't click Close button if any errors occur

Whenever you take an action in SourceTree, a progress dialog is shown over the repository view. Usually, the progress indicator is blue.

When an error occurs during processing the current task (e.g. committing files, staging files, merging, etc.), the progress indicator turns brown and an error message is shown in the dialog. Additionally, a Close button is shown.

Since I upgraded to version 1.6.1 earlier this week, whenever an error occurs, the Close button, even though clicked, does nothing; the dialog cannot be dismissed. The only alternative is to close the tab containing the git repository in question and then re-open the repository tab.

PLEASE NOTE: I checked for updates before creating this issue. As of 23-08-2014, version 1.6.3 is available. I installed this update in hopes that a critical issue such as this had been resolved. Unfortunately, the same behavior still occurs.

Platform:
Windows 7 SP1 with latest updates
IE11
Chrome (latest)
Firefox (latest)
.NET 4.5.1