I spent the best part of the entire day diagnosing and finally fixing this issue. The fix will be available shortly with Imagevue X2.7.
Some of you may be interested in the technical background of this issue, which is borderline of being a flash bug I would say, and I wanted to write it down since it stole my entire day:
# When does it happen? First of all, I spent hours trying to figure out just why a long text-page sometimes breaks and displays without a scrollbar. It appears that it almost only happens when the browser window/tab where the textpage is loading is unfocused (For example you are viewing a different webpage in a different tab or window, or another application). The error may then appear when you switch back to the window/tab where the textpage loaded in Imagevue.
# So why does this make any difference? It seems that new flash player version has some feature that it renders unfocused content much slower than flash in a window or tab that is in focus. This makes sense from a usability perspective, as it will decrease CPU activity from the flash player for content that is not currently being viewed. However, in our case, it had an adverse effect also -
# Why did this create an error with the textpage? Apparently, the flash player spends much longer time actually rendering a textfield with text when unfocused(as explained above). Therefore, the entire function that positions the textpage with background, mask and scrollbar simply fails because the textfield height value can not be read because it is not rendered properly yet.
# How to fix? Obviously, we could set a delay to make sure the text is rendered before we actually set the textpage. However, how to know when its rendering slow or rendering fast? We don't want to wait for a textpage to appear if it is in focus and the text renders fast. The solution was to add a function that checks the textfield height, waiting for it to change size, and once its changed, create the textpage.