This is normal operation for the POD.
When calling up an Amp Model, either in Manual Mode or in a Preset, the Model has a preset “Channel Volume” assigned to it. When the CHANNEL VOLUME knob is rotated, the “Channel Volume” will jump from the preset level to the level indicated by the knob. This level may go up or down, depending on the location of the knob. To keep the volume level from jumping up and blasting out the monitoring system, always begin by turning the CHANNEL VOLUME knob down before making any adjustments.
Once you have set the “Channel Volume” to your liking, it is possible to save that level to the Amp Model using the “Custom Save” feature of the POD.