That doesn't sound right to me either though. You enter a contract for 12 months at a reduced price. The company knows it will get 12reduced price. Now the customer wants to drop out after 7 months and you pay 7delta.
What you just have done is eliminate the monthly price. There can never be an annual contract anymore. That seems beyond silly. Is it really Adobe's fault for you trying to either be sneaky or simply malicious?
Presumably the current arrangement is some kind of creative accounting exercise though, and such a pro-customer policy might blow it up.