I know there is already an old feature request concerning that topic, but as I can't add a comment to it and I currently needed 3 hours to solve a problem at a customers label-printer that didn't printed my labels because doesn't accept landscape docs I do now open a bug-report.
It's not a good idea to change the paper orientation depending the dimension of the report.
As I said:
label is 159x51 pixel = orientation is actually portrait. But iReport makes landscape so the printer doesn't accept the job. I needed to change the orientation by hand in JRXML file with textpad to get it work.
Please let the user choose the orientation.
PS: Still using 2.0.2