Scrollbar oddity

Strange thing happened today. I have a vertical scrollbar which scrolls a canvas. It is set disappear if I make the canvas larger by dragging a grabbar. In terms of z-axis, the canvas is at the bottom and the scrollbar higher up. So far so good - normally, that works as it should.

Today, however, the scrollbar suddenly turned up missing - in the desktop app and also when running the corresponding project in the IDE (2023r4. macOS). Investigating, I could see no reason for its disappearing - its Visible property was True/False when expected, and its position in the enclosing container was as expected. No matter how I resized the canvas, the scrollbar didn’t show.

In the end, what I did was to go back to the previous project version, and clone it. That showed the scrollbar OK. I then ran Cornerstone and used it to go through the list of changes betwen versions and apply them one by one to the clone, checking for the presence of the scrollbar at each step. That gave me a second copy of the current project and with the scrollbar working as expected. None of the changes related to the scrollbar or its container, at all.

The only supposed difference that I didn’t try to apply was this:

#tag ViewProperty
	Name="Type"
	Visible=true
	Group="Frame"
	InitialValue="0"
	Type="Types"
	EditorType="Enum"
	#tag EnumValues
		"0 - Document"
		"1 - Movable Modal"
		"2 - Modal Dialog"
		"3 - Floating Window"
		"4 - Plain Box"
		"5 - Shadowed Box"
		"6 - Rounded Window"
		"7 - Global Floating Window"
		"8 - Sheet Window"
		"9 - Metal Window"
		"11 - Modeless Dialog"
	#tag EndEnumValues

which became this:

#tag ViewProperty
	Name="Type"
	Visible=true
	Group="Frame"
	InitialValue="0"
	Type="Types"
	EditorType="Enum"
	#tag EnumValues
		"0 - Document"
		"1 - Movable Modal"
		"2 - Modal Dialog"
		"3 - Floating Window"
		"4 - Plain Box"
		"5 - Shadowed Box"
		"6 - Rounded Window"
		"7 - Global Floating Window"
		"8 - Sheet Window"
		"9 - Modeless Dialog"
	#tag EndEnumValues
#tag EndViewProperty

I don’t know what that’s all about.

So in the end I have the scrollbar back but with no understanding of why. Comments appreciated.