Nice necro. I guess I'll share my fix for you guys. If you have any text saved to your windows clipboard outside of game, ANY text at all, it will prevent copying text from FFXIV completely. The best and only workaround is to remove the saved text from your windows clipboard. How you ask? Well it's simple. Just open an image in a new tab in your browser, right click it and select Copy Image. Make sure you are not clicking Copy Image Location. Once an image is copied to the windows clipboard it overwrites any text that was previously saved with that image file, thus freeing up the text spot on the clipboard. While the image is copied go back into game and copy whatever text you want and past it anywhere outside of game.

Some extra tips:
1. Copying text from FFXIV does not take up the text spot within windows keyboard.
2. As long as you keep that image saved into the clipboard you can freely copy and paste from FFXIV to any other program.
3. The second you copy any text from outside of FFXIV, the text spot will be taken and you will have to repeat the process of copying an image from your browser to remove it.
4. I highly recommend choosing from one of these two images to leave open in your browser at all times to copy when the need arises.