Fcisler, I checked the Sceptre model "X-42SV-Naga" (in my configuration), and sure enough (like Czzer said), it uses a custom input selection script/routine. In its dataset, I can see the following special commands:
o SetInputType PC
o SetInputType AV
o SetPCInput xx list (DTV,HDMI,HDPV,DVI,VGA,YPbPr2)
o SetAVInput xx list (Tuner,AV1,AV2,YPbPr1)
Note that for this model, the AV2 is present, and all the inputs are listed in the order you provided. I don't know what your particular model is but I bet if you use this "X-42SV-Naga" model, it will work. Just don't edit the device input settings (it uses a custom one).

As mentioned by Czzer in post 6 above, you probably should have phone support first instead of trying to fix it yourself, but now at least you know better (insight is always 20/20).