It seems that Safari iOS's latest "helpful" behavior, sliding the tabs and favorites bar out of sight, is changig the window size and so invoking reflow. Which moved what I was reading off the bottom of the screen. Scrolling down to find it again re-opened the tabs and favorites, changed the window size back, invoked reflow, and moved my reading point out of view above the window. Scrolling back up again - well, I'm sure you get the picture. Part of the magnitude of the issue was moving the page header (big green panel) from the top to the side and back again, also when the header was on the side the text font was larger.