Why does my kitten pee on fleece blankets?

I adopted a kitten that's about 5 months old from the local animal shelter (he was neutered there). After living with me for 2 weeks without accidents, he peed on a blanket I had over me while laying on the couch. A few days later, after washing the blanket, he did it again. Exactly same scenario, same blanket. Today I found out that he had also been peeing on a fleece blanket that was in his bed. He has only peed on these two blankets, which are both fleece. However, I have other fleece blankets that he hasn't peed on. What is his problem? What can I do to get him to stop?