At the moment I'm working on a website which is having some problems with minifying the CSS and HTML using Opcode: APC.
When I use "Disk" it works fine, but as soon as I switch to APC the problems start.
At first everything seems fine, but if you refresh a couple of times, sometimes it takes ±20 refreshes, the layout breaks and some style elements are displayed wrong. If you refresh again, it's back to normal again though.
It happens randomly so I don't have a clue where to look, but I noticed that if I refresh with two computers it happens simultanously on both the systems.