Buttons pressed in 1.8 (first noticed in 14w25a) remain pressed down for prolonged periods of time. Also, the button appears to be selective about which line of redstone it will power immediatley, and which it will power after many seconds.

As seen in the first two screenshots (note their file names) the button will continue to power lines of redstone long after it would would have shut off.

In the third screenshot, you can see that the north line of redstone is powered before the others.