All I can say is I'm now at 750 megabytes of RSS used for the process /usr/lib64/xfce4/panel/wrapper /usr/lib64/xfce4/panel/plugins/libxfce4powermanager.so 5 29360173 and it's quite slowly, but steadily growing. My version is 1.4.2, as obtained from the fedora 21 repos
Created attachment 5962 Plug a memory leak Can you try out this patch and see if it helps? It was the only leak I was seeing with the testing I did, but you might be hitting a different code path. Thanks!
Note: If you're pulling from git, that patch is already applied there.
Tested git head, and i could not leak more than 200KB memory over hours (as opposed to leaking 60MB before). Will further check by running valgrind, but I expect this specific bug report should be closed.