To answer your bullet points:

• Speakers DO NOT consistently pronounces these phrases differently.
• To native French speakers the two ways to pronounce them DO NOT sound
  similar (the liaison sounds weird).
• If they deliberately recorded the two sentences differently, then it is a mistake. As a native French speaker, I can tell you that no one will use a liaison in this context.

From what I read about the liaison rules (for instance in wikipedia), this case may be considered as an “optional” liaison but in practice, I have never heard anyone pronouncing it.