Can't Select Row or Column Headers AutoCAD 2013 Table

Mechanical 2013. I have created several new tables and modified them succe ssfully. Now it seems that I am unable to select the row or column headers of the newly created tables in order to modify them. When I try to select t he headers, it just deselects the table. If I click directly on the table, a caption with the table number and an asterisk preceding it appears (for e xample: "ACAD_TABLE (*T21)". What is confusing to me is that I was able to select the headers earlier in the same session, but can not now. When I cre ate a new table in this template, I have the same problem. However, if I cr eate a table in a different drawing, all works normally. That tells me that the issue is unique to this drawing. I am still able to select and modify one table cell at a time, but that is time consuming.I must have unknowingl y turned on/off some option or another. Can anyone please point me in the r ight direction? Thanks, Paul

Just as a quick follow up; this morning I saved a copy of the DWT file as a DWG and the problem disappeared. I then saved that DWG as a DWT; again, no issues. I'd still like to know why this occurs if any one knows. Thanks ag ain.