Totally agree, it is exactly what I was thinking at this exact moment...
I just clicked on the "Suggestion box" and saw your post ^^
When we use the tab preview, it is because we are looking for a specific tab out of a lot of other one... Our eyes are concentrated on the previews, and it would be much easier if the preview does not disappear when the mouse is hovering this "1 pixel" space at the top.
And, like caesyit91, I don't want to disable it.