I'm aware of this but one politicians verbal declaration is not an "agreement".
An "agreement" is something like the Budapest Memorandum that is signed by a number of countries.
I think I've watched this Pozner's talk a while ago, if it's the one where he argues that Russians are used to such "verbal agreements" more than to formal ones and it's all about "cultural differences".
I call it bullshit. Russian politicians perfectly recognize formal agreements when it suits them.