cannot apply threshold to t-coffee score annotation

Selecting 'colour by annotation' and setting a threshold for shading results in exceptions like the following appearing when the threshold is adjusted:

Exception in thread "AWT-EventQueue-2" java.lang.NullPointerException
at jalview.gui.AnnotationColourChooser.propagateSeqAssociatedThreshold(AnnotationColourChooser.java:684)
at jalview.gui.AnnotationColourChooser.valueChanged(AnnotationColourChooser.java:665)
at jalview.gui.AnnotationColourChooser$1.stateChanged(AnnotationColourChooser.java:84)
at javax.swing.JSlider.fireStateChanged(Unknown Source)

This exception happens for any sequence associated annotation where thresholds were not already defined - so disorder shading is not affected, but other kinds of shading (e.g. temperature factor) will be.