Some findings that refute Still-one's hypothesis (back to the drawing board!) : while using the iPad in vertical mode for about 2 hours, I encountered the following:

1) the search became unusable just like it does in horizontal mode. The workaround I found is that if you switch to the Queue screen, the search dialog will work. The only way to get search working on all screens again is to close and launch the app again

2) The controls may disappear just like they do when holding the iPad horizontal. Rotating the iPad 90 degrees to vertical doesn't fix this. Restarting the app is the only thing that has worked for me so far.

Screen shots below.

[Linked Image from dl.dropboxusercontent.com]

[Linked Image from dl.dropboxusercontent.com]