Why is each colon repeated in header field?

In Header.odt, the first page contains 5 paragraphs, styles Heading1…5.
These appear in the header in the 2nd page (№ 1). The last 3 fields are numbered, with each number separated by a colon (Tools>ChapterNumbering); why is each colon repeated — ‘::’?

Title: Why is header field underlined?
Details: why is each colon repeated?

Choose one, which should be answered.

Does not repeat on under Fedora Linux 34

from meta.xml:

<meta:generator>LibreOffice/$Windows_X86_64 LibreOffice_project/32efc3b7f3a71cfa6a7fa3f6c208333df48656cc</meta:generator>

→ You should have mentioned, that you are using a prerelease software, which most likely still has bugs and I can reproduce that on

Version: (x64) / LibreOffice Community
Build ID: 32efc3b7f3a71cfa6a7fa3f6c208333df48656cc
CPU threads: 1; OS: Windows 10.0 Build 19043; UI render: Skia/Raster; VCL: win
Locale: en-US (en_DE); UI: de-DE,   Calc: threaded

Yes, I used Version: (which is called a ‘release’ in the help window). So, I report that as a bug?

It’s not released - See Release Plan for 7.2 and LibreOffice Download Page, which has version 7.1.5 and 7.0.6 as released and current versions of LibreOffice as per today.

> So, I report that as a bug?

yes - I’d suggest to do so.