Thank Alex, here is the information you requested.
1. No, the problem is exclusive to the new Safari Beta. (Firefox, Nightly, Chrome, Canary, Opera etc. work fine)
2. No, I cannot replicate the issue on this site.
3. It is not a caching issue. (I have tried disabling caching, tried clearing cache... even tried CCleaner)
4. It does not seem to be linked to optimizations nor compression.