Ey, you are right... but something has changed.
It seems that now iPad request the desktop version by default forums.developer.apple.com/thread/119186
And it seems that the tap and hold only activates when a mobile is detected (what is no longer happening in iPad)
And if you select to load the mobile version, the sliding from outside of the window for displaying windows is confused with slideover functionality in iPad :-)
If the tap and hold would be active even in desktop version would do the trick right there :-)
What do you think?