keterys
First Post
It actually isn't in Heroes of Shadows, where this power appears.The Summoning Keyword's duration limit is ALSO in those same books.
There _are_ a bunch of summons, all of which include an encounter length duration note, except for this one, which specifically excludes that line, says it lasts until you use the power again or it's destroyed, and has text noting that a necromancer almost always has its summon with it, since it lasts until it is destroyed.
Rules arguments are hardly new things to D&D, because the people writing it don't write with a particularly legalistic bent, nor particularly care as long as the game works fine without going to that length. So, again, I heartily encourage you to submit that this power should be errata-ed for unclear duration alteration, if you feel strongly about it.