On the antenna jack, when I initially tested it with my Wellbrook ALA330S during the day time I found exactly the same thing, but I would not say signals were reduced to "Zero"...they are merely attenuated. At night the radio overloaded using this method but pushing the plug all the way in cleared things up.
I therefore think they have the proper amount of attenuation built into the Aux Ant jack for the SW sensitivity of this radio.
Also I find its AM sensitivity much better than the G3...it's as good on AM as the E5/G5 were which the G3 never matched. I don't believe it is a rebadged G3...there are too many differences.
I agree the muting sucks.
But this radio has many pros and cons,..I'll be posting a full review soon.