It is normal behavior for Fathom. You can actually capture the ball to get your full ball multiball restarted, but it comes at a price of losing scoring while trapped, and possible drain to next ball...
The ball can also be release by the side set of drop targets (color correct).

Yeah, re-locking balls during multiball and the drop targets not resetting is normal behavior. If this happens, you can hit the rollover in front of the ball lock saucer to release the ball. Or, like themadman said, you can his the correct color of the side drop targets.

--Luke

The star rollover won't release the ball, it's normal, it only give 50,000.
To get the multiball again you must hit the left drop target coresponding colors.

themadman is spot on, the ball will re-lock for both saucers. You can re-release ball by finishing color-matched drops on the left; blue for lagoon, green for cave. No other way to re-release ball during your turn. Star rollover will not re-release ball.

Really? My bad then. I guess I need to play more Fathom.

Sorry for the misinformation.

--Luke

Your Fathom is faulty and you should sell it. To me.