Default Can't copy to System/app :(

I've been trying to copy the clear weather apk to system/app using root explorer. I set the folder as RW. It allows me to rename something to .Bak but refuses to let me copy an apk into this folder. I can't figure this out. Never seen this happen before.

Any suggestions?

Sent from my SM-N900W8 using XDA Premium 4 mobile app
Follow me on twitter @Blue1k ...thephonecollector