I had the same thing. Pressing the superkey caused the application loading and the only resolution was a reboot. Phones are on a different VLAN to PBX. It's a reoccurring problem.
Reoccurring problems indicate a problem of somekind... could be firmware. software, network, hardware, or user (although in this case I don't think so), and could be an indication of a larger issue, these should be investigated and resolved. Get support involved if needed, open a web ticket and attach a system SD package as a place to start.
Sometimes these are really dumb things too... we did an upgrade of an 11 site cluster from 4.2 to 7.1 a month and a half ago, no real issues for 2 weeks then the customer started saying that on random 5330 phones on random nodes the screen saver of the set would turn on by itself, turn it off and a few hours later or the next day it would be back on, and then seemed to gradually go from a few phones to over a hundred in a couple weeks. We were stuck, tech support was stumped, nobody could figure it out... then I went into the All IP Telephones Inventory form one day to look at something completely different and noticed that some of the 5330's had an odd firmware load, half were 4.x.x.x and the other half and all the 5340/5360 sets were 6.x.x.x firmware. Long story short, after the customer manually rebooted 150 or so sets, the problem was gone, the whole time it was just the phones didn't pull firmware during the upgrade for some reason.
Alternative moral to this story... Just because a customer says "Yes, we rebooted the phone and it is still doing it" doesn't mean they REALLY rebooted it.
