It's not a bug, it's a (missing) feature
Basically I was too lazy to cope with the (separate) progress display code for the old-style download system.
To be honest, I'm not sure why sv_fast_download 0 is still an option. It provides limited feedback for the clients, is less configurable/throttleable for the server owner, iirc it copes badly with high ping clients, and of course takes bare time to actually download anything. On top of that I don't believe any issues have been encountered with it that weren't also present with the old system. The only reason I can see it being useful is as a compile-time option if you wanted to run a q2-compatible server.
