I have a 'big board' that my husband made, that is used ONLY for my quilting projects. I noticed, I'm thinking in its first 6 mos of life, it did have an odor. To me it smelled musty.
So I thought, musty, wet.
Since then, when I notice water of any measurable amount gets on the board, I run the iron over it a few time to get the water evaporated as soon as possible. I have not noticed the smell since I started doing this.