Tech Priests no longer leave between Sectors?

Played a quick normal siege for the accolades before the reset - noticed that my team were buying new Tech Priests on wave 5 and thought it would be wasted.

After we got off the lift for wave 6 the Tech Priests all reappeared with their remaining cooldowns in the new sector.

When did they add this? It's not in the notes for the latest patch.

Also, despite the 'nerf' to the Tech Priest income we were still swimming in coins, though I only stayed to wave 15.