jmol 12 memory leak viewer object not garbage collected when viewer closed

Symptom: Turn on memory monitor, and watch it increase after importing projects containing structures and then closing all windows. For less dramatic effect, open and close the same structure several times (if its a really big structure you may see some difference).

JvisualVm tracing shows that the org.jmol.viewer.Viewer object seems not to be garbage collected, and when initialised with a structure state, it seems to hang on to the string representation of the state.

Will need to check that Jalview is not hanging on to any references to listeners associated with Jmol.viewer.Viewer (console, script window, etc).