Adding non breaking spaces:

  

into a table column makes the wiki-markup view to be rendered very slowly. As the number of spaces increase, the wiki-markup and preview modes become unusable. The markup does not load.

If the mode has been set to use "Wiki-Markup" by default, the markup loads fine. Though once switched to "Rich-text", same behavior is experienced when switching back to wiki-markup mode.

To replicate use this markup on a page:

|| COMMENTS                                                     \\ ||

Save and then open the page and switch to "Rich-text" and then back to wiki-markup mode. Notice that the markup does not load.

Tested on Firefox and Safari.