Forgot to post an update. It sure was an issue with light. As soon as i have moved it to the location with actual sun, the yellowing disappeared. This has started to showing on my other trees also.
The bigger problem was that trees were infected with spider mites (i think that is what they are called in English language) and i wasn't aware of the issue so i have reacted a bit late.
The result was bunch of really ugly leaves with brown spots and one dead branch (that i loved dearly) on my Acer ginnala. Will sure be more careful and more proactive in the future.