LAFuture.collect crashes when futures are resolved out of order

I'm using LAFuture.collect from Lift 3 Snapshot to collect 3 futures into one. It sometimes throws an IndexOutOfBoundsException at me.
The reason is this line:

val vals = new collection.mutable.ArrayBuffer[Box[T]](len)

which defines the result array. Later, when future 2 is satisfied before future 1 it tries to insert it at a index that does not yet exist, thus throwing the exception.
The fix I found was to pad the array with Empty's and then later in the foreach write a Full into it.

Here's the repl that produces the exception:

scala> new collection.mutable.ArrayBuffer[Int](3)
res0: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()

scala> res0.insert(2, 4)
java.lang.IndexOutOfBoundsException: 2