i Had the same problem with CM10.2 & CM10.1 , Even though it works fine with every other Rom i tried ! (Like Liquidsmooth , AOKP , Evervolv ..etc)
i tried a clean install and every other solution but i had no luck
Evo 3D - Unlocked - S-Off - HBOOT : 1.49.0007 - Radio : 11.77.3504.00P_11.25.3504.06_M - 4ext Recovery.
I am having a problem with wifi in all CM11 Kitkat Build , the same problem is when finish flashing Rom the wifi works for a bit until the phone detects Network (2g or 3g) . i tried putting the phone in airplane mode directly after booting so my wifi stays connected until i remove airplane mode . after it detects the network (MTN coverage) , the wifi will not search for wifi networks anymore !