Signal Viewer Breaks Interval Parameters

[dm-p]

Observed in 1.6 - in Vega-Lite, if we're using interval parameters, these work fine until we enable the Signals tab in the debug pane. When we do this, the selection doesn't work as we expect, and we then get the following error in the Logs tab:

We have to exit/re-enter the editor (which will continue to perpetuate the bug if we have the Signals tab selected) or re-initialize it.

This is not a blocking issue, but it is incredibly frustrating to build visuals with this functionality when the bug is active.

Root cause seems to be when the unit signal generated by Vega for these parameters is updated/re-read. The initial value (when the Signals tab is selected) works OK.