Takes forever to load in IE sometimes

I got this weird bug or something. In IE it sometimes takes about 2 minutes to load the fckeditor. And after that it works fine without problem. I sometimes also happens on other pc's that never loaded a fckeditor before.

Only seems to happen in IE7 and IE8. Never in firefox, but I can load the Demo version on here without problems and fast. Even more weird:

I delete all history of IE en reboot the pc, but then it stills loads fine and fast. What could possibly be causing this weird behaviour?