First thanks for the great work.

I'm new to this project so perhaps I miss some experience but..
When setting numFmt of a column: sheet.getColumn(3).numFmt = '0.00', the formatting works as expected but the column gets invisible. (using MS Office Excel 2010).
Only if also the width is explicitely set: sheet.getColumn(3).width = 10 the column gets visible again.

Is this by design? Wouldn't it be good to warn for this issue in the docs?