I noticed today that a drawing I was working in had columns on by default in MTEXT. As there did not seem to be a way to turn this option off on the Ribbon and only an option to turn it off in the MTEXT editor once activated I had a root around for a setting (using the premise that AutoCAD has myriads of settings).
The setting to control MTEXT columns is strangely enough MTEXTCOLUMN. Set it to 0 to have no columns.