I am assuming you got your themes from bplay? I had the same issue where my themes would not work in landscape mode. I contacted bplay and this was their response:
"Hi, We are aware of this issue. It is occuring due to the OS (Operating System) 5.0 release from RIM and it is an OS issue, not a theme issue. This impacts all themes for the 9500 & 9530 which are running 5.0 OS in landscape mode. It seems the theme works in Portrait Mode, but in Landscape Mode, the OS will not rotate the graphic, or skin some icons. We have alerted RIM of this issue & it should be resolved in the next OS release."
Not the answer I wanted, just sit around and wait for RIM to push the next OS revision. Hopefully, they address it quickly because it is something that is getting more annoying by the day.
I am running the elle theme and while not a fix I already had StopTilt. I hate the rotation on my home page so all I do is disable autorotation.
Like I said it is not a fix but for all those who dislike the autorotation on the homescreen like me it works.
One thing I did notice though, StopTilt used to lock the Look Screen in whatever setting you had on the screen just before you locked the phone. It doesn't do that any more.
Posted from my CrackBerry at wapforums.crackberry.com
Change the wallpaper on your theme. You can not use the default theme background. Usually you can get the default background to use as your wallpaper and your good though.
Change the number of rows in the homescreen (Layout: Rows). Then change it back to two.
(You do this by pressing the menu button and selecting options in the menu)
The changing of rows part has to be repeated once each time you reset or change themes.
