Active page bar in TOC navigation

I have a tree view drop down menu TOC. In a chapter, there are several pages. Some have page headings and some represent continuation pages within a page context, e.g.

Colour principles

Introduction (Include in TOC = true)

Colour perception (Include in TOC = true)

Colour perception1 (Include in TOC = false)

Bla bla

When I click on introduction, the Introduction text is highlighted. If I go to next page, the Colour perception text is highlighted in the TOC. When I then go to next page, the highlight jumps back to the Introduction entry.

I can see this is done in the Lectora generated HTML, in the page init() function, where it does

...

else ObjLayerActionGoTo( 'a001_colour_principles_colour_perception1.html' )

setTimeout( 'trivUpdateTOC( "a001_colour_principles_introduction.html", "a001_colour_principles_introduction.html", 1 )', 500 )

...

It should be doing

setTimeout( 'trivUpdateTOC( "a001_colour_principles_colour_perception.html", "a001_colour_principles_colour_perception.html", 1 )', 500 )

Does anyone know how to for the TOC handling code to highlight the previous 'visible' page rather than the first page in the chapter?