I reinstalled everything from zero and now it's fine. Control center 1.3.0 gives me crash but 1.2.9 r3 is fine. Anyway with latest VTi 4.1 my Leadtek Winfast Dongle Gold works like charm. I didn't even have to install a driver. It automatically detects the stick as a secondary tuner when I plug in. Looks like VTi 4.1 contains drivers for some popular sticks. The funny thing is that it doesn't contain driver for the Sundtek MediaTV Digital Home.
Now I feel that it was an unnecessary purchase from my side because the Leadtek dongle can act as a DVB-T tuner without any additional modification or installation. I've noticed only one thing where the Sundtek is better: it shows the signal power and signal quality accurately.