I've been building my position over the last week and noticed...

I've been building my position over the last week and noticed something interesting (to me at least).

I've placed 4 buy orders across a number of days that I've put in before open at .006c when the buy side was sitting at .005c and sell at .006c.

Every time I did this there would suddenly be a sell amount at .005c for the exact same amount (or a few shares more) as the buy order I submitted for .006c

My question. Why?

I'm not complaining as I've managed to keep my average buy price bang on .005c but did find it interesting.