When parameters have long names, refreshing the joint marginal panel sometimes leaves parts of those names visible, after a different selection of traces has been made.
Select a number (>5) of parameters in the joint marginal panel
Go to trace panel and go back to joint marginal panel
Select a smaller (<5) number of parameters
Short bits of the original parameter names are left on the panel
When parameters have long names, refreshing the joint marginal panel sometimes leaves parts of those names visible, after a different selection of traces has been made.