ToME: the Tales of Maj'Eyal

I've found the effect of the talent 'step up' always disappeared when any cooldown was finished (especially when using the dagger 'Spellblaze Shard', which has a three-turn-cooldown effect). Sometimes it even appeared and disappeared at the same time, and I haven't taken a step yet. Is it a bug? If it's not, how does it work?

What's most likely happening is that the Virulent Disease (you get from Spellblaze shard) comes off cooldown and is immediately used because an enemy is taking blight damage (from a disease etc), which counts as an action other than movement so it removes Step up