This is not unique to Swindlers; it can happen with any foe in the game (including wizards in PvP). I have had it happen with fire elves in Wizard City all the way up to Youkai and Oakheart in Mooshu, and yesterday Zora SteelWielder in Dragonspyre. Many times during a duel, the game will add a point of two or health to one or more of the participants right at the beginning of a turn (I have no idea why). You can see your own health bump up by a point sometimes in your red crystal ball just as your cards come up at the start of a turn. Most of the time people just don't notice it. The time you do notice is if you defeat a foe by only a point or two, and the extra health brings them back from zero (when they fell over) up to one (when they magically reappear, ready to fight some more). KI knows about the issue; I don't know if they are planning to change it. Just think of it as a strange side effect of using magic.