When toggling from lateral to horizontal edit form in Proofreadpage environment (nsPage into wikisource), #wpTextbox1 keeps its default height; this behaviour is unconfortable, since often the last part of text needs scrolling of the page to be edited, and image of the page scrolls on and disappears from screen.
I added a simple personal patch to reduce #wpTextbox1 height when choosing horizontal view, and to restore default height when returning into lateral view, but I think that this behaviour should be automatized.