I have attached 2 screenshots.
The first is right after editing formula, the second is when I click on the table to view the formula right after editing. Note I can highlight the 'invisible text'.
After further investigation with trial-and-error, using Mechanical 2011- I tried creating the problem with a new drawing (using acad.dwt), but could not duplicate the problem with a simple table and lines. It must have something to do with the way my drawing template is set up (all drawings are created from it)
Trying to save the file as an older file type does not help.
If I use Mechanical 2012- I can not duplicate the problem. Tried saving it using 2012 (saving as 2011 file), but Mechanical 2011 still has the problem.
It is evident that somehow the combination of M2011 and the way my drawing is setup? is the problem- though I have no idea if/how this is correctable.