When folding is toggled so that 800 line buffer is folded to 80 lines (with the window height being 50 lines), the scrollbar slider dosn't change its length and remains of the same size as when the buffer is unfolded. Is this behaviour correct? Shouldn't scrollbar slider size depend only on visible lines and change its size when the number of visible lines changes (e.g. after folding)?
This behaviour is intentional. From the maillist:
This is because computing the size of the scrollbar thumb would require going through the whole file and computing the folds. That can be very slow in a large file.