Yup I can confirm I have the same problem since the recent update. It happens as soon as I try and edit a sign and then I can't type any text, or interact in the Inventory screen. I can still use my keyboard for movement and basic character interaction
I've actually worked out what specifically breaks the ability to type text...
Step1 - open sign
Step2 - edit sign
Step3 - press ESCAPE ( bug activates )
Workaround step3 - use your mouse to click somewhere other than the sign
Step3 is the critical point. From this step signs can't be edited and the user can't enter text in text boxes. However, if the mouse is used to exit the sign rather than hit the escape button on their keyboard then the bug doesn't activate.