haven't noticed a change. any chance the target unit was magic immune? (opidians or obisdian golems or similar?)

No. Tremor was placed on units, and ruffians. It said paralyzed for three turns, but the next turn it said paralyzed for 0 turns and it moved. 

My apologies, I did not advance the turn, just checked that the spell was castable. After rechecking, it's exactly as SBF shows, 2 units appear as Immobilised for 0 turns on the second turn, others show no status effect.

I've reported this bug before.

When you cast Tremor on an army, it says "Immobilized for 3 turns."  End the turn, and next turn it'll say "Immobilized for 0 turns." and they can move.  Effectively, Tremor lasts for 1 turn.  Unless you cast it on an army of 1, then it lasts 2 turns.

Freeze has a similar problem, but not nearly as bad.  Freeze also says it lasts for 3 turns, but it only lasts for 2.  It counts down the number of turns immobilized for, but once it gets to 1, the army can move.  So, you cast it, it says 3 turns immobilized, you end the turn, it says 2 turns, you end the turn, it says 1 turn, and the enemy can move that turn.

In short:  Tremor lasts for 1 turn, Freeze lasts for 2 turns, both say they last for 3 turns.

Honestly, if Tremor worked as described, it would be overpowered.  They should probably just change the text so it's not misleading.  They should fix Freeze, though, since it's got a 5-turn cooldown.