Oops.
Quite embarassingly simple.
To answer my own question it looks like there is a check box in QT preferences which checks for upgrades automatically (whether you are at the latest level or not).
//System Preferences/QuickTime
Somehow when I re-installed, this box came back checked whereas it had not been previously.
Could have sworn I went through all the preferences but its always good to go back and check these things again.
Its usually something simple...
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