Steps to recreate:
1. Create a brand new character (6E, Heroic or Superheroic, 15 points, 0 matching complications).
2. Add a Multipower framework. Set it at 10 active points (which costs 10 points of the 15).
3. Add a 2d6 Blast (Fixed, no modifications), which is 10 active points and 1 real points, for a total character cost of 11 points.
At this point, it gives a warning about the character exceeding the points available. Presumably, this is because the AP of the Multipower and the AP of the slot add up to more than 15 points, even though the actual points spent does not.