Disabled Dragon Turtle still untargetable [Investigating]

In a recent game, my opponent had Dragon Turtle, which was disabled due to my Suppression Bonds. I also had Savior of Ollenbock and two other creatures. I attacked, and Savior did train, but I never got the prompt to allow me to exile Dragon Turtle, even though Dragon Turtle was disabled.

An odd element about this is that later in the same game, my opponent had another creature in play, and when I attacked I did get the Savior prompt -- and it allowed me to select Dragon Turtle as the target. It seems the bug only prevents the prompt from showing up in the first place, it doesn't prevent you from selecting the Dragon Turtle once the prompt is already there.