ArgumentOutOfRangeException when calling RankedMap.ElementsBetween(lower, upper)

[sandimschuh]

I get this Exception when calling ElementsBetween with identical values >0 for lower and upper.

ElementsBetween(0, 0) --> works
ElementsBetween(1, 1) --> throws

my RankedMap contains 10,000,000 items with 1000 distinct key values.

Stacktrace:

bei System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
bei Kaos.Collections.RankedMap`2.<ElementsBetween>d__55.MoveNext()
bei System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
bei System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)