Table of Contents Formatting Issue

I have a VBA project which compiles separate documents (chapters) into a single planning book document. The book uses different chapters depending upon the project.

Anyway, some of the chapters are of such a length that I've placed a Table of Contents (TOC) at the start to aid in navigating the chapter.

I use the "Selection.InsertFile FileName:=myFileName, Range:="", ConfirmConversions:=False, Link:=False, Attachment:=False" method to get the chapter content into the book document.

This works well. However, I've noticed that on some of the chapter TOCs - which look perfect in the chapter document - have the dots switched to tabs. Not all of the line item dots are converted to tabs just a few.

I'm kind of at a loss as to what's going on and how can I prevent it from happening. Anyone have any ideas?