Why did my credit score change?

So my credit score was holding steady at around 825 from March through September. Then in October, it dropped to around 800 for seemingly no reason.

- My credit utilization has remained the same.
- My account age has only gotten older.
- I haven't missed a payment.
- No inquiries since February.
- Credit mix is good and unchanged.

I can't figure out why it would drop unless there is a period of time in which the type of accounts I pay on is factored in. Basically, in February I stopped paying on credit cards monthly as I had been but still left them open. Maybe it took until October for the fact that I stopped using the cards frequently to kick in?

Thoughts? It shouldn't matter in the short term, but in 18-20 months I'll be looking to buy another house and want all the help I can get on a good interest rate. From what I can tell, 800 is a cut off for some lenders between very good and excellent credit and could affect my rate on a mortgage...