I was playing Day 12, when I moved my repulser back and the creeper got through. And even though it had no creeper valve, in continued to grow. This is a bug, as it should have never grew bigger once the valve was killed.
What was the density of the Creeper at the time? If there's enough of it, it will try to expand as much as it can, even in the absence of an emitter.
It sounds like the creeper was particularly dense, and depending on the situation, the repulsor may have been compressing the creeper into a small area, and when you moved it, it spread out again.
it's possible... I guess although my towers were at the very bottom of the tube that contained the creeper... Maybe just my fault!