Update: I figured out how to set the tab stops in LibreOffice. I tested it with a simple text file in LibreOffice (instead of using an ODT file type). This worked correctly. I didn’t have the weird behavior I was experiencing in ODT files. I also just tested it with DOCX files and got the same behavior as I did with ODT files. So the solution is obviously to use simple text files with LibreOffice for creating my lesson matrices.