You were right, there is a small problem with a transparency. Maya and other renderers usually accept transparency map where black is transparent and white is not. RPR is doing it opposite way, so I have to invert all transparency textures myself. Usually I'm doing little trick like that by inverting it in effect section of texture file but it is not working with RPR, so only photoshop is the way to do it. I attached screenshot to make it more clear.