wmfsm tryes to show free space of devfs, sysfs, devpts, usbfs. thease file system ins't displayed whit df -h command but mounted and visible thrue /etc/mtab or mount command Reproducible: Always Steps to Reproduce:
Created attachment 30810 [details, diff] fix fix of this issue
Uhm, you reversed the patch file, rediffing... Uhm, there are more 'system' filesystems to be added... OK, in Portage, thanks for the submission! Please test it and let me know if it works good for you... Also sent the patch to the package maintainer upstream.