Copy an Paste issue

We have a character rig that uses expressions on both legs. The legs are identical but the expressions are different because they are picking values from different nodes/columns.

When I copy a pose from the left leg to the right leg using CTRL+C, CTRL+V it works as expected, unless I paste it at frame 1. If I paste at frame 1 then ToonBoom will paste the expressions from the left leg on the right leg replacing them.

It gets worse when using CTRL+B (Paste Special, using the setting in the attached file) because it will always replace the expressions.

We have just upgraded to Harmony 20, but this issue was present in older versions also.