well, that is one of the nastier bugs i've tracked down in recent memory. very satisfying.

observed phenomenon: if your first interaction was to drag page down
(i.e. move viewport relatively up), the first slide got bent out of
shape -- jumped to really tall height. it didn't occur without the
slides nested within the pages, so now i'm now setting slide height
(formerly always 100%) by pixel height of window at same time as page
height is set. seems to work. i don't grok it all, but it seems to
work. sO iT gOeS