In the past couple C3D versions, I've had these random borders show up in my simple tables. I have a table for my legend and another one I use for a list of references. I use no borders for these tables but sometimes when I edit a cell somewhere in the table, the random border will appear. I remove it and then sometimes it reappears again later. It's usually the top line of the second row, second column only but occasionally it will be when I add a row into an existing table. I'm not sure if this is a bug or some weird setting I'm missing.
I would check your cell styles. If the cell style is getting changed when you edit the cell, that could be the culprit.
If you don't get a satisfactory answer here, post in the AutoCAD discussion group as well.
I'm not intentionally changing any styles at all. It seems to happen after different things like sometimes if I move a table or sometimes if I add a row or even just edit the contents of one cell. It's really random and doesn't happen every time but of course I usually don't notice it until after I've printed 10 sets of something. I think it's a bug but thought I'd throw it out there and see if anyone else has seen it. Thanks!
Oh, and thanks for the ACAD suggestion. I'm always buried in C3D so I forget about that forum.
I have the same problem, only it happens every time I open the drawing I remove the border line and save then when I close and open the drawing the same lines appear in the table. I do not even make any changes to the table.