Sanctions don't prevent the short-term behavior. Russia thinks that it is winning in Ukraine - thus the one-sided deals, it isn't about the other side accepting it, for Russia it is about Russia forcing such a deal, and it always includes lifting of the sanctions as a key element of a deal that Russia is trying to force because even with traditional lack of long-term vision they understand that the sanctions are crippling the country. They think that winning the war, forcing such a one-sided deal, is the only way to get the sanctions lifted "cleanly", and any deal with concessions, etc. would look less than victorious and would probably have the sanctions lift incomplete/incremental and boggled down with conditions, etc.