Solid line at bottom of the cell - how to get rid of (not obvious!)

Ok, I have pesky solid line at the bottom of one field (bottom of the field with 6.80 in it..





I cannot figure out where it has come from or how to get rid of it!



here's the properties for that particular field...







Any ideas?!!!



When I delete the column it appears somewhere else...like whack a mole!

Solid line at bottom of the cell - how to get rid of (not obvious!)