After a recent upgrade on Kubuntu, Kate editor (v3.8.5) shows odd lines under the entire text of previously created simple text files. New files usually have only the first line underlined. Maybe if I knew what this is called, I'd be able to find something. It does the same in KWrite, so it could be something in whatever the two have in common. Highlighting is set to "None'. Here's what it looks like:
EDIT: Thanks, but that command doesn't seem to have any effect on this. This is KDE 4.8.5. In another example, the lines change a bit: