That is as I would expect, based on my experience. Next time try a straight slurry repitch (I schedule my lagers for when my beer is ready to rack, so it literally is re-pitching minutes after harvest). Also I wonder how many generations out before a difference shows up, if any. The most generations I pushed it to on a yeast strain was a bit over twenty repitches on a WLP 800 house lager brew. Never a problem, but eventually I just gave up using the yeast to move on to something different....