Putin has always said that any peace talks would be based on the premise that borders would be frozen as they are now (or, rather, were prior to Ukraine's incursion). Having Ukraine in Russia, effectively ceding territory if they are frozen now, is something he's not prepared for. The situation shows the lack of any real peace effort on his side - he's prepared for (temporary) peace if he can keep the land he's grabbed and Ukraine gets nothing, but he's spitting the dummy now that, by his own previous "peace" conditions, he stands to lose land. Peace talks are a two way process, but this development just shows his calls for peace were a sham, designed to grab territory and give nothing in return.