The Bartenura, in his commentary to Kelim 27:3, notes that the rules concerning the admixture of cloth with sack, sack with leather and leather with matting only apply to those specific combinations and not to admixtures of cloth with leather, leather with matting or sack with matting. In stressing this, he notes that, when it comes to those things, they don't combine, since "המחברן בטלה דעתו אצל כל אדם".
I can't figure out what this means, and have never seen it anywhere else. I am guessing that it translates to something like, "[as for] the one who combines them, his mind (his intention?) is nullified by (?) all".
I am taking "mind" (דעת) as the subject, since בטלה is a feminine verb, but the whole thing looks very strange to me. Does anybody know what it means?