Can confirm that I'm getting this exact same bug on OS X 10.9.5, Transmission v 2.92 (14714)
Added a torrent via the web interface and an hour later it's still verifying at 79%. As soon as I opened Apple Remote Desktop on my MBP and remoted into the machine and cmd+tabbed to Transmission, it started downloading normally.
A bit more about my setup, this is a Mac Mini which I have running Transmission and Plex (client and server). The client runs in the foreground with Transmission just downloading in the background.