I haven't heard that one. And, to be honest, it doesn't really make much sense to me, because the modern Russian constitution is a pretty nice document overall, guaranteeing all the good stuff etc. It's just that it's never really been followed.
This isn't new, either - e.g. the 1936 Constitution of the USSR (adopted under Stalin) was considered a very liberal document for its time. Freedom of religion, freedom of speech, and freedom of assembly were all guaranteed, there was strict separation of powers, universal franchise with secret voting, and so on. Ironically, most of the people who authored it would end up in gulags or with a bullet in their head within a few years of its publication.
That still sounds off given that Russia didn't have any constitution at all until 1906, after the first Russian revolution. Getting one was the primary demand of Russian liberals throughout the 19th century, and was stubbornly resisted by the monarchy because a ruler bound by any kind of constitution is no longer a proper "autocrat", which was an important ideological distinction for the Empire.
Even when it comes to informal, customary constitutions, the only restriction that was universally upheld was that the reigning monarch had to be Eastern Orthodox (if they weren't, they ipso facto didn't have the divine right to rule). Everything else was ultimately subject to the Emperor's whim.
