Maperitive: parsing of any mrules file fails after saving it

In Maperitive I have a strange problem, that seems to make any reloading of mrules files impossible:

steps to reproduce:

I am running Maperitive v2.4.3 on mono 6.12.0 on Arch Linux.

• launch Maperitive
• load random area from overpass api
• go to Map->"Edit rendering rules", which fires up gvim on my system
• save the unchanged file in the editor

Reloading the mrules file fails with the following errors:

ERROR: Unexpected token 'VALUE' (line=14, col=15)
ERROR: Unexpected token 'VALUE' (line=12, col=13)
ERROR: Wrong indentation (line=15, col=3)
ERROR: Wrong indentation (line=16, col=3)
...

The rules file is the "Default.mrules". At first I thought, my vim would automatically replace some whitespace on saving, but that seems not to be the case. I downloaded the original versions of the files again and initialized a git repository in the "Rules" directory, to monitor any changes, which doesn't show me any changes after saving the file again. Most strangely, restarting Maperitive and loading the mrules file again fixes the problem, until I am saving the mrules file again.

I am totally clueless about this. It is quite a major blocker in the workflow, since Maperitive has to be restarted after every change to the rules file, so that parsing it works again.