My Scrum Problem...

With my present scrum model, I am finding a classic problem of requirements Vs scrum model. We are dealing with a web application, in which a new theme/skin is proposed and stories are built around that.

The problem comes when the designer thinks of changing the present proposal and proposes a new skin/theme. With this changes, the previous stories are becoming invalid. 

The real problem starts , when QA defers verifying/closing the defects from one sprint to another due to lack of time. I know this is not the correct method in sprint, but QA just can't do it.This deferring happens especially for defects araised at the end of the sprint in one particular story.

I have list of defects which are invalid now; Well, QA can close them as invalid but lot of time is getting wasted while QA tries to close them in next sprint where QA has to discuss with dev before closing each defect. QA often gets message from dev such as "hey those are invalid defects due to yesterday's change'! We are not going in that path" while trying to reopen the defects. The entire scenario is chaotic. 

I am not sure , whether this is normal in scrum or something fishy.. Solution should be from Scrum Master or from Product Owner