Update: This has been reverted until a later patch release when they can get it fixed. No more Invoke in random pools for the time being. (Source) The text below has been preserved.

A welcome change for Galakrond Decks was put into place in Hearthstone's 17.0.0 Patch - Invoke Cards can randomly generate! This will also work if you've managed to steal or clone a Galakrond and it became available in your hand or board.

However, there is currently a bug! This bug puts Invoke cards in the random pool for all decks. The team is working on a fix.

Quote From Chadd Nervig

Saw some questions about Invoke cards getting randomly generated… There was a change to this in 17.0.

Pre-17.0: Invoke cards aren't in the random generation pool.
Post-17.0: Invoke cards are in the random generation pool, ONLY if you're a Galakrond deck.

Update: The above is the intention, but it looks like there's a bug with this, and it's including Invoke cards for everyone, not just Galakrond decks. We're working on a fix, sorry about that!

what if you aren't a galakrond deck, but burgle a galakrond and play it?

Technically, it cares about Galakrond ever being in your deck/hand/board at all. (Source)