Hmmmm not sure about that one as mine does show the owner as "trustedinstaller".
Weird thing I've noticed also is that the live tile for the Windows store is working (it shows things like "red stripe deals") but when I click on it it refuses to stay open, green screen then minimizing to the task bar. I think I've basically tried everything there is to try and I feel that the more I mess about with my laptop, the more damage is probably being caused.
I've also noticed that the "PurgeCaches" message has changed slightly it now says on second line "the application didn't start" really!!!!?
Should we term the new message to be progress I wonder?
You could check in the Registry as described on this site in the middle: http://www.optimizemswindows.com/fix-error-ms-windows-storepurgecaches-while-resetting-app-cache-windows-8-1/
I just checked on my own machine and this is what permissions for SYSTEM should look like. Oh, and the blank space in the menu is where my log on username normally appears.
To get the Permissions for Packages menu, right click "Packages" in the "Repository menu on the left and go to "Permissions".