Epoxy fizzing

Have you ever seen anything like this before?

I'm putting the final touches on a tiller we are building for Koan. Unfortunately the fir that it's made of splinters horribly, and so it did when I drilled a hole for the tiller extension. I decided to fill the hole with epoxy, and I was planning to re-drill it. I taped one side of the hole, made up a tiny batch of penetrating epoxy (GitRot) and filled it up. Almost immediately when the epoxy filled the hole it started bubbling! My only theory that doesn't require a bogy (an acid or contaminant or something): because the tiller is varnished, the penetrating epoxy is displacing air, which cannot leave any other way and it comes out in bubbles. I don't buy it. I gave up stirring after about 10 minutes, knowing that this was not quick-set epoxy and therefore it was not about to get hard anytime soon. In the the end most of the epoxy bubbled out of he hole, though it did coat the exposed fibers, which was all I needed. The hole now looks like this, with the metal insert in.