Hello,
Your inventory windows should already remember their last position. The position of most UI elements are saved when you close the game. The lock on the skillbars is just preventing you from accidently moving the bars or moving or removing the skill buttons - the actual position of the bars is saved when you close the game just like other UI elements.

I think what you might be seeing is when you open certain other UI windows that automatically open your inventory too - like the Auction House, Extract, Vendors etc. I think in those cases the inventory windows get repositioned to the right side of the screen - but the next time you open your actual inventory yourself it should be using the saved position as normal. I guess it is kind of annoying. I remember wondering if I should remove that repositioning stuff and just always use the saved position but it could end up with your inventory windows hidden behind the other windows.

Oh yeah that could be a big problem if we lock it and it got behind other windows