It's up to the DM to apply some common sense to get at the RAI. The editors used natural language and omitted most of the niggling details. If the editors had been as picky in the descriptions of the magic items, the DMG would have been as thick as a dictionary (and about as readable). The spell descriptions in the PHB are generally very specific and call out every detail in well-defined game terms such as Bonus Action and Reach. So relax - the effect of the item is exactly what the DM says it is. DMs don't have to rules-lawyer and have no interest in min-maxing. But MM and DMG content are written as guidelines for the omnipotent DM.
Here's the key: the WoC editors were super-specific about spells and class features, because players are clever little maniacs who will scour the PHB looking for every advantage and synergy that they can. DM's have absolute authority over Magic Items.
