Confirmed as fixed. Cheers!
Edit: I have been reading more in portrait recently due to the ability to not pan too much, as opposed to landscape where there's essentially no option to pan. For instance in portrait a 600 x 1000 file essentially allows you to see an 'overlap' of 600 pixels in the middle, which is really helpful when reading non-standard panel layouts (eg small panel on top, big panel at bottom). This is as opposed to landscape, which, if you read a 800 x 1200 file, essentially you get no 'overlap' between the two presses of the page down button, which means that if you have odd panel sizing/big dialogue boxes you'll need to flip between the two halves of the page which gets incredibly annoying.
Ah, it also occured to me that English runs horizontally, whereas Japanese and Chinese run vertically. As I read mainly non-english manga this compounds the 'overlap' problem for me.
Hence mangize is a lifesaver for me - I get to output my manga in 600 x height, and be able to pan downwards with overlap between top and bottom panels, enabling me to read dialogues that run vertically downwards for half a page.