I found that with the latest nightly builds over the last week that my CSS based dynamic menus disappear if I scroll the page some. I've created a test html page to illustrated this. When the page loads, the menus behave correctly. The menus are created using <ul> and CSS styling to hide the sub-menus. When you hover over the <li> element, then the sub-menus appear. After the page loads the menus work as expected. When moving the mouse over the menu item, the sub-menus appear. However, if you scroll up a little, then you find that the lower sub-menus begin to be clipped? If you scroll too much, then the entire sub-menu is clipped and is invisible. It must still be at the correct location because the links in the sub-menus are still active. You just can't see the submenu? The z-index is set to 100 to make sure the sub-menus should always be drawn above the text. With the latest builds some draw clipping error appears to have crept in.
Created attachment 12019 [details] test file with simple dynamic menu on top left of page. To try out this test page, hover the mouse over the single menu item on the top left of the screen. All four sub-menus should appear. If you scroll the page up a little, the menu should not change location (position:fixed). Now, if you mouse over the menu item, the sub-menus will appear clipped or be entirely invisible, depending on how much you scrolled.
I just did another test. If the <ul> menu structure is not fixed to the screen (position:fixed), then the clipping issues do not appear? This seems to be tied to using position:fixed.
*** This bug has been marked as a duplicate of 11452 ***