Textures can't be overwritten while in-game

Hello!
I'm making a texture pack, and when i modify my texture(s) using Photoshop,
i can't save over the file i'm working on (from time to time).

Sometimes i can save the image and then tab to minecraft, hold F3 and press T and the texture is updated, but most of the times i get an error prompt saying the "file is already in use". But if i wait for like 2-5 minutes i can save it again (without closing minecraft)..
This makes it very tedious for us texture makers, it worked flawlessly with the old terrain.png, though i had this same problem before when editing parts of the GUI etc.

The only way to solve this right now is to close minecraft, save image, re-open minecraft and log back in, or wait 2-5 minutes.