Infected being frozen has 100% only been on this patch, none other. We previously had infected that constantly moved even when there was no one near them, which used up server memory (or something to that effect) .58 seen the removal of infected whilst they were being worked on. When .59 came out we got them back, but with the added bonus of them being frozen as a sign that someone is in the area (400-500m range of infected). Glad to see @eugenharton on the case but I'd have thought this would be something the Devs would have been aware of by now.