I'd bet both the yeast and bugs are working. The bugs usually take a long time (months) to really sour a beer so I'm betting the yeast are swelling your pack.
Edit: well the bugs can sour sooner depending on what they are. I'd still say just brew with it and see.
You can probably tell the difference if you took out a sample and plated it to see the different colonies, but it might be hard to tell between them. Not worth the effort in my opinoin.
"People should not be afraid of their governments. Governments should be afraid of their people." - V
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