what`s browser do you use?
In my Opera all work as intended, just little motion for hovered links.
Firefox 3.0.11 - flickering Buttons
Internet Explorer 7.0.6001 - flickering when moving pointer up and down
because of "left 1px" (or top 1px) in the css-file the button is mvoed 1 px to the right-down so if you hit the first pixel of the button, the pointer will not be on the button when it is hovered, so the hover-effect is disappearing
on disabling the hover the button moves 1 pixel top-left and so the pointer again is over the button and activates the hover-effect
and so on ...
firefox is everytime checking for pointer-position so the button is flickering all the time as long as the pointer is on this pixel
internet explrer is only checking for position when moving, so the button is either hovering or not, but will change all the time as logn as you are moving the mouse on this regarding line of pixels
don't have other browser so unable to check there
Edit: This FF glitch is adressed here and has a fixed status (2009-07-01). Will probably be patched on next update for FF 3.5.
there is no change of "font-face" in the hover-formatting ? so no FF glitch here ?