There is a bug with tactical buffs, that they do not end when tactical combat is over, but instead they stick around until the specified number of turns is used up. However, this is not a problem with the burning blade spell itself but any buff spell. Since the game only takes into account the specific gamemodifiers, it doesn't seem to know that burning blade has been cast before. It just keeps adding more and more game modifiers, without ever realizing that it is duplicating anything. For some spells, this is probably not desired, like in this case of burning blade where you probably can't just keep setting your sword on fire. Yet for other spells, it makes perfect sense to allow for stacking buffs or debuffs. Personally I would like to see them update the xml to allow a mod maker to specify whether a spell is stackable or not, and for them to associate spells and gamemodifiers so that one can make some kind of dispel magic or spell specific debuff.