+ AA6YQ comments below
I would be surprised if it truly IS rf on the cat cable since this look very much like a CAT command to adjust the frea. I'd think rf on the cat cable would create a CAT error by disrupting the communications betwen the PC and radio...
I suspect that WSJT is actually moving teh TX freq to "center" the tx signal in the passband...
I thnk you mentioned that below 1500hz it does not shift?
can you go over 130w if the TX freq in WSJT is below 1500 hz ?
I know wsjt CAN adjust the vfo to shift the TX signal in the audio passband to improve tx audio (avoiding audio filters in the radio.) might be what you are seing...
+ Adverse behavior that only occurs when transmitting and that disappears as RF output power is reduced is almost always the result of RFI.