The [SHIFT]+[CTRL]+[C] seems to be system global (meaning, you can press it anywhere without the QAP being active).
It opens the customize window of QAP.
[SHIFT]+[CTRL]+[C] is also used in
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Everything: From the search results, copy full name to clipboard (name=full path).
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Dopus: From selected items in lister copy full path to clipboard
Both of the above are not system global so they don't interfere with other applications.
Bot when QAP is running it interferes with the above 2 aplications.
I understand that you could re-assign keyboard shortcuts but new users or users who tend to use their apps as default as possible (especially regarding hotkeys) might get some interference with this. Also
I think [SHIFT]+[CTRL]+[C] is used in other applications as none-system global actions. (the 'C' is also often used as "Copy" action).
Those actions (I think) are very often used in day-to-day use, compared to going into QAP customize mode through the above hotkey (once user finished setting-up QAP, it will be more used as menu-mode).
If for important reasons the default keyboard combination can not be set to something else, I understand.