Never saw a follow-up to this. I had the same problem, but through Word, but I was able to resolve it without creating new files/rebooting.
The problem appears to be related to you being signed in with your LiveID, and if you have the Office Live Add-in as well. In my scenario, I would
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sign in through workspace.office.live.com, and open up my document.
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Word would start and I would start editing the doc.
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My laptop would sleep some time later. Then I'd wake it up and word would tell me it had lost the connection.
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Attempting to close/open the file shows "locked for editing" by me.
My solution:
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Sign out of live workspace through your browser (this invalidates your LiveID on your browser)
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(important) Sign out of live workspace through Word! This is an option in the "Open from Office Live" or Office Live save menus, and can be easily missed.
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Open the orignal document again (either through your browser or Word) and the doc is editable.
I only did this once, and didn't reproduce it. hope it helps someone else.
For the Office Live team - if this reproduces, it's a really crappy, unintuitive experience. There's no way a normal user would understand they are actually signed in twice. Really need a feature that allows you to override the lock if you are the owner of the file.