After some recent maintenance, our SQL Server machine began to create/display a blank command window for the SQLAGENT90.exe
Something had been changed, but it was difficult to track it down...there seemed to be nothing on the internet about it.
A post at http://www.windows-tech.info/15/89dd3fae1ba00d46.php finally revealed with the answer. During maintenance, someone/thing had set the service property 'Allow service to interact with desktop'. As stated in the post the fix is as follows...
Under Computer Management --> Services -->SQLAgent (select this instance) and double-click to openup the properties, move to Logon tab and remove tick on 'Allow service to interact with desktop' and restart the service.
I figure that others may experience the same thing at some point, so I thought I'd share the fix.