Option "Allow a different input sources for each document" behaves erratic

I use multiple languages, and want to use option

Language & Text > Input Sources > Input source options > Allow a different one for each document.

But it is totally broken and erratic.

It does not remember each document's or application keyboard language, but instead appears to switch them randomly.

E.g. I open several tabs in Safari, open one of them and switch keyboard to Russian.

Now switch to another tab - it is U.S. (OK), switch back to previous tab - now that tab is U.S. too (Why?).

Even worse - open Terminal, switch to Russian, click System - U.S. (OK), click Terminal again - U.S. (Why?)

Sometimes it remembers the window' keyboard, sometimes does not and switches it randomly.