Hello,
this is the expected behaviour, a comment from Development:
It is a standard wait for a double click. If a modifier key is pressed the double click wait is ignored. That key was added just for that purpose. Cubase’s behavior is to ‘open’ things with a double click: a part is opened into an editor on a double click not a single click. If there is no click wait time, then multiple selections would be hard to implement with standard platform rules.
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The ref. number is CHEST-1795 - I’m pretty sure we have more than one entry about this, and more recent as well. I will add its ref. number as well when I manage to find it.