To reproduce:

Create a page with the following Wiki Markup content:

Switch back and forth between Rich Text and Wiki Markup tabs ... note that it works fine.

Now, in the Rich Text view, put the cursor at the end of the table, on the very next line (cursor blinking just below the table). Click the insert-link icon and select a wiki page. Click the Wiki Text tab and see that the content looks something like this:

Click back to the Rich Text tab and see that the "IT:My Page" link has been sucked into the table, and now constitutes a third column.