-snip-
Checking the DPs only for validity does not mean performing the entire work again. Kangaroos are jumping from one point to another based on visited x-coordinate, and as soon as kangaroo lands the x-coordinate with the determined pattern (i.e. coordinate with 25 leading zeros -----snip-
As far as I understand it is important that the DP is from a real kangaroo walk.
The difference:
As soon as a kangaroo hits a point (a point that is not qualified to be a DP by bitmask) that has been visited by a kangaroo of the other type, their walks are synchronized and the next DP they find will definately result in a collision and PK is found.
This is not the case with randomly selected points in the range that fullfill the DP bitmask criteria.
It is possible that there will be a collision with these kind of "not real walk" points though.