Custom page size: creating a PDF in Mac

I'm working with Mac OS 10.8.4, MuseScore 1.3 rev. 5702. I need to produce a PDF from a score that uses a custom page size - 9 x 12" US (228.6 x 304.8 mm). Every time I use the save as... or save-copy feature and simply save the file as PDF it appears to save it with height and width reversed (i.e. as 12 x 9 / 304.8 x 228.6). I cannot figure out if there is a setting to adjust this and/or what kind of workaround is available. Thanks in advance for any advice.