Yes, I've observed several oddities over the years with CCs and highlighting. However, it this case I think the issue is with how the triple click selection works (which could also be considered buggy). Before going forward, your sample document contain 2 content controls. One titled "Finding" containing the highlighted text nested in another CC (otherwise empty) also titled "Finding". I'm not sure if that is intentional or not.
Using that document, triple click the text and run:
Sub ScratchMacro()
'A basic Word macro coded by Greg Maxey, http://gregmaxey.com/word_tips.html, 9/29/2018
MsgBox Selection.Range.Start & " " & Selection.Range.End
lbl_Exit:
Exit Sub
End Sub
The return is 0 and 125
Now just select the text as you have done as a work around and run that code again. This time you get 2 and 125.
While the selected range appears the same, clearly the triple click method is picking up a part of the CC that can't be edited.
To add a bit of user control, I'll suggest an edit to Graham's method:
Private Sub Document_ContentControlOnEnter(ByVal ContentControl As ContentControl)
If MsgBox("Remove hightlight?", vbYesNo, "REFORMAT") = vbYes Then
ContentControl.Range.HighlightColorIndex = wdNoHighlight
End If
End Sub
Or if you want less intrusive control. Just click in the CC and run:
Sub CCReview()
Dim oCC As ContentControl
On Error Resume Next
For Each oCC In ActiveDocument.ContentControls
If Selection.InRange(oCC.Range) Then
oCC.Range.HighlightColorIndex = wdNoHighlight
If oCC.Range.ContentControls.Count = 0 Then Exit For
End If
Next
End Sub