this still happens just randomly for me,( 10.6.3) when I open up LP. its so annoying. not like I ever selected to hide main window.
there should be at least something that says 'your main window is hidden, click here to show'
even 3 years later i was wondering why the f** i couldn't hear midi notes all of a sudden. no idea how it got this way, but I had to turn back on the midi out. this question saved me from anxiety attack.