This is the problem (known to exist in 1.4.2) of most of the space
in the young generation being shifted back and forth between
eden and from-space AND only full collections happening after
one of the young generation collections where most of
the space has been shifted to from-space. In a young generation
collection eden, from-space and to-space are resized.
When the next young generation collection is done,
the space would be shifted back to
eden. In a full collection eden and the
survivor spaces are not resized so the
space is left in from-space.