Was dryer fabric softener properly used? 

If your dryer contains Steam cycles (available on some models), use of a fabric softener sheet is not recommended with Steam cycles because it may cause staining on clothes. See your Owner's Manual for tips on using your steam dryer.

Fabric softener sheets were designed to be used with damp fabrics. Add a dryer fabric softener sheet at the beginning of a cycle. A fabric softener sheet added to a partially dried load can temporarily stain your garments. 

Fabric softener stains are usually temporary. To remove the stains, rub the stains with detergent, and then re-wash the garments.