I have the same issue, but it only happens in one document. I click anywhere in a table, and the entire document highlights and will not allow me to insert any text. This document is mostly a series of tables with instructional text in them and graphics.
I have turned off all of the sticky key settings and have pushed the shift key several times as described, all to no avail.
All I am able to do is to move the cursor with the arrow keys which unhighlights everything and allows typing. Again, only in one document.