Wiki Markup - Bold Text doesn't render mid way through a word

Description

The bold markup will not render correctly (in visual editor or comments) when it's part of another word.

Steps to replicate

Add wiki markup to an existing word mid way through the word (for example, the "es" in "test".

Expected results

The "es" is bolded.

Actual results

The "es" is not bolded.

Workaround

Insert a tag like color into the markup.

Test cases:

*test*
t*es*t
t{color}*es*{color}t

Produces:
test
t*es*t
test