Hash mark markdown headers do not preview correctly when using 4 or more hash marks

https://daringfireball.net/projects/markdown/basics :

To create an atx-style header, you put 1-6 hash marks (#) at the beginning of the line — the number of hashes equals the resulting HTML header level.

My markdown:

##xxxxxxx Utilities

####To trigger an update to t

Result when browsing Stash (blurred to protect IP):

Rendered version: