I see two possibilities here. One is that you have a 64bit Windows 8, and 32bit BitTorrent; and the Task Manager has problems in identifying traffic from within the 32-bit VDM. If you have a 64bit Windows 8, you can test this hypothesis by installing 64bit bitTorrent.
The other possibility is that bitTorrent is playing tricks with WFP, the Windows Filtering Platform (ex LSP, Layered Service Provider) in order to make good its claim to "optimize bandwidth usage":
BitTorrent auto-adjusts bandwidth usage, based on your network and
Internet connection, to ensure fast file delivery. Your downloads run
in the background. Which means they’ll never slow down video chats or
In that case, you could try fiddling with bitTorrent's bandwidth usage options to see whether one of those is responsible.
The fact that user Hardy's installation appears to be working proves that there are no inherent problems in either Windows 8 or bitTorrent; this must be a configuration problem (or maybe a conflict with some other installed software. In that case, maybe unistalling bitTorrent and re-installing it, therefore "on top" of whatever network driver and service chain you have, might fix the matter).