While editing a skin while in-game (Testing: Saving the model will reload your model while in testing in-game mode) you cannot type the letter t while naming a new cube. It instead opens the chat dialogue for in-game. In order to get around this bug you can copy the letter t from the chat and paste it in the name box.
Video Displaying the bug:
https://user-images.githubusercontent.com/39831475/147253823-548712c8-9b0d-40e5-ab37-d364fe83b57d.mp4