The “Change status to” dropdown on the view issue page used to select the first option in the list as the default. Choosing the default value in this way isn’t particularly useful because workflow states usually progress than regress. The dropdown default value used to look something like this:
Recently this behaviour was improved so that the default value of the “Change status to” dropdown is selected as the next available status beyond the current status. For example, if the current status was “feedback” the default value is now “acknowledged” instead of “new”:
If no higher status is selectable then the highest available status will be selected.
You can expect this minor change in the next minor 1.2.1 release of MantisBT.