After almost 4 years of use, one of my testers noticed something strange with my update panels.
Let's say I have a display mode and it takes 100 pixels in height. The user then switches to edit mode and the updatepanel updates. The window is now 500 pixels in height. The user clicks save and it turns back to display mode, which is only 100 pixels.
Now the dom only takes 100 pixels, but there still is a scrollbar all the way to 500 pixels. If the user shrinks the screen down to 100 pixels, he/she will still see a scrollbar, despite the fact that there's nothing down there anymore.
What the hell is causing this and how do I fix it? It's like the updatepanel doesn't tell the window it doesn't need all that height anymore.
Sounds to me like your control maybe using visibility="visible|hidden" instead of display:"none|block".
It also may just be that your edit mode is too big for its fixed height container. Try not constrain the outermost container so it can grow with the dynamically changing internal content.
The visibility property determines whether a given element is visible or not (visibility="visible|hidden"). However, when visibility is set to hidden, the element being hidden still occupies its same place in the layout of the page.