In my development career, I've come across my fair share of voodoo (as anyone from CMC Markets will attest to). We once found an issue in Apache Tomcat that had the best minds we had, and the entire inforweb, stumped.
This one takes the biscuit though. Every other build I do takes twice as long for graphics to load. I've tested this about 15 times on the trot now, and it's remained consistent. Do a build; graphics load in 19 seconds. Do another build without changing any code or content; graphics load in 55 seconds. Do another build; graphics load in 19 seconds.
I'm sure there's some rational explanation for all this, but by crikey it was fecking annoying until I figured it out.