This is actually semi-expected behaviour but it causes confusion when a member tries to help another by posting a shortcode in a reply.

In many cases, the shortcode clashes with a markdown code and as a result, an incorrect shortcode is posted. Typically, the shortcode begins with an asterisk, which is converted to some kind of effect. The result is that the member trying to be helped will actually be hindered, because they will try to use the incorrect shortcode and be puzzled when it does not work.

Experienced members may know that they should post the shortcode in backquotes to prevent this. But I believe it's essential that we should get this right so that it happens automatically.

To do this, I suggest:

that prior to handing the message over to the markdown processor, the message be filtered to detect any shortcodes (using the list at https://community.giffgaff.com/d/6471662) and globally replace them with the same shortcode in backquotes. Those shortcodes will then continue to be displayed correctly after passing through markdown
note should be taken that the above list includes irrelevant spaces for display purposes. In many cases, members will cut and paste from that list. In other cases, members will type them in to the message and are unlikely to include the spaces. The filter process should therefore endeavour to catch the shortcodes regardless of embedded spaces
existing messages, and new messages posted by experienced members, may already contain backquotes so care should also be taken to ensure these are not doubled
consideration should also be given to what happens when an existing message is edited, or is requoted in a further post, to ensure that the correct shortcode continues to be displayed.