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theducks -
Curious - can you recall when the accelerator keys were added to the Notify Slide-ups. I'm pretty sure they weren't there when that feature was initially implemented -- IIRC I complained they were mouse only artefacts.
For reasons unknown even to myself I had Alt/Y assigned to extract ISBN - Y rhymes with I

That shortcut was of course, configured long before Notify Slide-ups saw the light of day
There's no check in Prefs->Keyboard to prevent Notify Slide-up accelerator keys being used for other purposes. Maybe if there's a Notify pending it should get priority.
I teach old people how to use computers, many of whom have arthritis and HRS, so like me they're mouse averse. Most of those that have calibre also 'inherited' my shortcuts. I'll send them an apologetic Easter email
Added : see ==>>
Bug #1439888 “Slideup Notify Accelerator Keys”
BR