If Ezren plays a “Display” card (i.e. Orb of Frost), then plays a spell which triggers Expanded Spellbook (and uses it), the “Display” item will be moved back into his hand without any kind of check.

Works regardless of the card owner. If e.g. Seoni plays the Orb on Ezren's check, it will return to her hand if Ezren looks at his deck.

This is still a live bug.

 

Related (I think?) I also managed to have Lini play Agility, then Ezren played a spell (on Lini's turn) and used Explanded Spellbook and ended up with Agililty in his hand!