libreoffice writer page border has a gap

Using LibreOffice for the first time.

I want a thick coloured border around the edge of every page.

Setting that up in Format>Page>Borders

However, there is a gap at the bottom left corner.

What am I doing wrong here?

LibreOffice 6.0.7.3

Ubuntu 18.04.4 LTS

Not in version: 6.3.6.2 (x86); OS: Windows 6.1.

Confirmed for your configuration but this doesn’t happen on Ubuntu 18.04 using ppa:libreoffice/libreoffice-6-3 (currently distributes Version: 6.3.5.2) - Hence it seems to be a problem of the specific version distributed by a base install of Ubuntu LTS 18.04. Consider using PPA.

Works fine in 6.4.4.2 (x86_64); Fedora 32; KDE Plasma

I kind of remember this was an issue an ancient releases. Try to upgrade to a more recent version.

Added ppa as suggested by Opaque in the comments & updated to 6.3.5.2
Problem has gone.

Thanks all.