As the patch notes specified, your client will now remember the position of the retainer inventory window. Trying this out myself I found a problem however. When interacting with the retainer bell and choosing the option to browse the retainer's inventory everything works as intended. The retainer's inventory opens up, you can reposition it, and after closing and reopening it again it remembers the position of the window. However the problem lies when you choose the option to sell your retainer's inventory on the market board. I don't know about you, but I personally never use the option to ONLY display the retainer's inventory. Every time I open it up with the added window for selling things on the market board which in addition to being able to sell things allows me to move items between my own inventory and that of my retainer. And here is where the problem lies. For some reason the retainer's inventory window is placed in the exact same place as your own inventory window. So if you open your own inventory you are not able to see the retainer's and vise versa. Since the windows overlap perfectly, you are only able to move the retainer's window away when your own is not opened, and if you do that you will find that when you open your inventory again its position has moved with the retainer's. If you open and select your own inventory window you are able to move it away without moving the retainer window with it, however this means that every time you decide to use this option you then have to reposition your own inventory window back again afterwards (since the next time the retainer's inventory is opened in this fashion it will again be in the same position as your inventory window is now). Myself, I like to have a tidy UI with windows always in the same positions, and this is making it very hard to keep it that way. Additionally it means that I can no longer check prices of items in my own or my retainer's inventory with ease, while moving items between the two since I have to choose either the option to look at my retainer's inventory (no overlapping windows), or the one to sell my own or my retainers inventory (only one inventory window visible). I am not sure whether this was done intentionally or by accident, but it would make MUCH more sense for the retainer's inventory window to open in the same spot as it does when you ONLY want to look at the retainer's inventory as well as when you're trying to sell his items on the market board.

tldr; Choosing the option to sell your retainer's inventory on the market board places his inventory window on top of yours, which makes it almost impossible to also move items between the two.