Looks like water damage to me. Especially on that band.

I am thinking maybe when you filled the humidifier there was a bit of excess water on it and it dripped onto your smokes.

I would recommend you toss out the solution and the foam and get some beads. They worked great for me before I switched to active humidification. Much lower maintenance compared to the foam humidifier that I started with.

www.heartfeltindustries.com
www.cigarmony.com

Two great places to pick up beads or "The Puck".