Did you upgrade to 1.12 or install fresh? (no hkey_current_user\software\xolox entry in your registry)

and

Did you set the upload speed to "max" in your preferences?

The first I ask because the 'rules' in 1.12 are based on a connection type, and if you upgraded, the registry entry for broadband or modem isn't created, and I don't know what, if any, effect that has. The second I ask because the options page is a little misleading. There is NO limit to the speed of individual download segments, but setting a higher upload speed will let you download more segments at once. this number is Upload speed (K/s) * 2 so if you don't think you'll b\need to be downloading more than 20 segments at a time, then select 10 K/s as your upload speed,