Fun with D&D 5 Magic: Detect Glibness

D&D 5 has the spell Glibness, an 8th level transmutation spell. This spell makes "magic that would determine if you are telling the truth" indicate that "you are being truthful."

Okay, fire up that "detect lies" spell again and get that mage back in my throneroom. 

Mage, repeat this back to me word-for-word, "I am the king of this land."

It's a funny difference and oversight in the D&D 5 spell compared to the Pathfinder version, which works a little better with a "no discernible lie" qualifier. Sometimes when you rewrite a spell for simplicity, you lose the language that made it clear and work correctly in the first place. This is the reason why the 3.x line of D&D spells just bloats with special cases, exploits, and other silliness.

It really is a question of "how much do you want the referee to rule against cheese?" versus "how much do you want to handle special cases?" - and ultimately an ease-of-use thing. With too many special cases, it's likely time to rewrite the spell than spend a half-column of page space explaining something that's broken.

With D&D5's spell of Glibness, it's not broken, it's just poorly worded in that if you take this literally, there's always a way to detect it by forcing someone to tell you something you know is a lie. A good DM would call this BS and disallow it, but rules-as-written it's pretty hilarious.

I might allow it once if a player came up with this clever tactic on his or her own, and then disallow the spell and lie detection method because it's been posted to the Internet and now everyone does it.