Data grid cell formatting strangeness

I'm trying to format some cells in the data grid control and it's not working as described in other posts I've found here. If I put _hello_ in a cell, 'hello' is italicized instead of underlined. If I put [hello] in a cell, 'hello' is underlined. [], [x], () and (x) all work as described. What am I doing wrong? I'm a brand-new user using 1.6.40 on Win XP Pro with Flash 10.0.32.18 installed.