Well . . . My Old Jubilation clone got put on hold this past weekend as lightning caused me to get called out for some repair work. Anyway, when I “popped” the pair of WY1028 packs to make twin 1 gallon starters. One pack was hideously swollen after 8 hours, the other . . not so much. Not the first time I’ve had this happen, but have always wondered why the differing personalities with the identical yeasts that have the same date codes.
???
Interesting question. I’d suggest emailing Greg Doss at Wyeast and see if he has an explanation.
I’ve heard of this before. My LHBS said it was why they only sole White Labs.
Because if the White Labs vials were different, you’d never know? 
I did . . as of yet, no response.
You jest, but it probably does cause a lot of trouble for LHBSs. In reality, the yeast is usually still good, and they should probably be making a starter with it anyway.
Ah . . I did just get a very nice response from Greg . .
Unfortunately, I do not have a good answer for this situation other than
it should not happen. Assuming that the nutrient packets in both
packages (identical strain and lot#) were ruptured, they should expand
the same. CO2 production is an indicator of culture health, so it may
be possible that one of the packages was compromised at some point. If
the package showed signs of swelling and then was put into a starter,
there is less reason for concern. If the package was to be directly
pitched into wort, additional inoculum may be necessary.
Yeast is a living organism and is subject to a loss in
viability/vitality over time. All cultures leave our facility meet
our rigid specifications, allowing us to guarantee the quality and
performance of our products. If you have concern over the culture,
please return it to your retail shop for a replacement culture.
I hope that this helps.
Cheers,
*Greg *
As it turned out, the starters took off just fine and so did the Old Jubilation fermentation. Wyeast comes through again! 
And the smack pack concept is proven pointless yet again ;)