2 things come to mind Sonar. Is your dummy load a known good one? Not a cheap one. A good one. And also know they can vary in impedance which will skew VSWR readings. Read the manual that wavrider posted about your WM1 meter. The 2nd issue is RFI. It's on page 2, #4 paragraph. The other issue about dummy loads is on page 1, paragraph D, which talks about dummy loads. Read both very carefully and if you are using a cheap dummy load or on that has been damaged from being dropped or overheated, this may be your issue, or it could be the other issue stated. That is if you are connected to the antenna. Hope some of this helps and you get things straightened out.
You may also want to try using a radio that will dead key at least 4 watts or more. I know the WM1 says it can read at power levels as low as 1/2 watt, but I have found that too low a power level and some meters won't read correctly. Might be why your MFJ meter isn't reading correctly. Again, that or your dummy load night be bad or just off as well. It's definitely possible.
I would try using a stock radio that will dead key at least 4 watts before I sent anything out though. Just some food for thought. Hope you get all your issues resolved. Have a good one and I truly hope some of this helps.