With page size set to 11 inches wide by 8.5 tall (landscape dimensions), exported images do not fill the full image/PDF page. The exported image occupies the upper left ~2/3 of the image. It is also apparent that the first page is exported at a slightly large scale than subsequent pages, as the "1" page number and a bit border remains visible behind subsequent pages in PNG exported images (which have transparent backgrounds.)
I do not know if this problem predates my recent changes to the export code (patchset 291). Instructions with page dimensions of 8.5 inches wide by 11 inches tall (portrait dimensions) still export properly.
Example LDraw file including LPub meta commands.
Example exported files are available here:
http://anoved.net/images/lpubbugs/2951249/1_page_1.png
http://anoved.net/images/lpubbugs/2951249/1_page_2.png
http://anoved.net/images/lpubbugs/2951249/1_page_3.png
http://anoved.net/images/lpubbugs/2951249/1_page_4.png
http://anoved.net/images/lpubbugs/2951249/1.pdf
I can't reproduce this error in a made-from-scratch test file, but it still occurs with the 1.ldr test file. I have been trying to export it without various meta commands in an effort to identify the source of the problem, but have been unsuccessful.
However, I discovered that it even occurs when I restore portrait page mode (8.5 x 11 instead of 11 x 8.5). The page contents appear shrunken to the top half of the page. So, I think this means it is not a landscape layout issue, but a different problem. Example: http://anoved.net/images/lpubbugs/2951249/1n.pdf (1.6 MB)
Raw model with no LPub metas except for 11 x 8.5 page size. Exports fine! Problem is something between this and 1.ldr