IPv6 client behavior

I working on implementation of my IPv6 client. I have done support for stateless and stateful IPv6 assigning. But I am wondering what is right/expected behaviour of client when IPv6 network configuration is changed at router/firewall.
Let say that was assigned IPv6 address from stateful DHCP server to client (M flag=1 at RA message) and lease time did not expired. But I received later RA message with M flag=0. That means configuration of firewall was changed from stateful to stateless. Should I continue with current IPv6 address from DHCP server till lease time expire or just goes to SLAAC address instantly? Same thing when is used SLAAC address but RA message with M flag=1 is received later.

Thanks for a comments.