I've seen some strange audio metering behaviour in the past so delved into it a little...
I created a sequence with two 'standard' tracks and cut in mono tone to both tracks.
I panned A1 to the left (in the clip mixer) and A2 to the right
I increased the gain on the A1 clip by 10dB for identification purposes.
When I mute A2 I get the following on the meters:

and everything appears as I would expect. A1 is a stereo track, but is panned left so only has audio showing on the left leg - and this is replicated on the A1 track mixer meter and on the master output meter on both the track mixer and the main meters. All good so far.
When I unmute A2 and mute A1 I get the following:

again all as expected, this time on the right leg.
When I unmute A1 and listen to both tracks I get the following:

Now the master output metering is correct but I do not understand why the right leg of A1 clip & track mixers are showing level, nor the left leg of A2. Bug?