I think this may be a rehash of an earlier bug report (from version 7.460, I think):
When I attempt to download large files via HTTP, say, a 900MB ISO file... I get maybe 80MB or so of the file (it varies somewhat) before IE or Firefox saves the file, claiming it's done... but it's not, the whole file did not download. This is with the HTTP proxy enabled, running in transparent mode; THe AV settings are set to skip scanning a file over 100MB in size, so the AV should not be the problem -- the typical Astaro Download page is not displayed, the download just starts, as it should with it set this way. Downloads from the same sites on 7.404 worked fine. I checked all the logs (I mean everything). The only event I can see that coincides from a time standpoint with the downloads dying is the up2date daemon checking for a pattern (or system, can't remember now) update... and there wasn't one available, so it wasn't like a lot of bandwidth was consumed, etc. This sounds kind of like what I recall reading about earlier.
I'll post some log entries up here when I get time to pull them from the test system I was using.