Weird underscore emphasize intepretation



I am confused between the following two interpretations:

<< Input:
foo: bar baz_quux

HTML output:

foo_: bar bazquux

The first _ is combined with the third _, not what I intended obviously.
But I put a space in front of the colon (or leave the colon out), it
suddenly is fine?

<< Input:
foo : bar baz_quux

HTML output:

foo : bar baz_quux

Any ideas/work-arounds?
Kind regards,

PhD Student @ Eindhoven | email: removed_email_address@domain.invalid
University of Technology, The Netherlands | JID: removed_email_address@domain.invalid


That is really weird. I have no idea.