Semantically correct would be to insert a Zero Width Non-Joiner (U+200C) anywhere inside the magic prefix http://.
When placed between two characters that would otherwise be connected into a ligature, a ZWNJ causes them to be printed in their final and initial forms, respectively. This is also an effect of a space character, but a ZWNJ is used when it is desirable to keep the words closer together or to connect a word with its morpheme. (https://en.wikipedia.org/wiki/Zero-width_non-joiner)
The Zero Width Non-joiner is 'semantically correct' because it does not add any further information, other than 'please do not join these two characters'. Apparently, the Markdown script to highlight URLs does not ignore it, as it should be doing when parsing 'purely textual content'.
If you want to extract Strings that begin with http://example.blah.com/, you should...
... which we can test by inserting it in between some other Markdown markup sequences:
> this is a test to see what happens to *[ZWNJ]*bolded*[ZWNJ]* textrenders as
this is a test to see what happens to *bolded* text