Incorrect style nesting on headings

[NeoEGM]

This is a bug report.

Name	Value
DokuWiki Version	Release 2018-04-22b "Greebo"
PHP Version	7.3.10
OS	Linux
Web Server	Apache/2.4.41 (Unix) OpenSSL/1.1.0l PHP/7.3.10
Docker image	bitnami/dokuwiki

Details:

Given the following simple page code:

<markdown>
# This `is` a `test`

This is text
</markdown>

Instead of the expected heading:

This is a test

It renders:

This a 

Thanks!