Unknown error occurs when using a Text tag in commands

When using the Text1, Text2, Text3 and/or Text4 tag(s) on signs in commands, it seems to ignore the tag(s) and display this error message:

An unknown error occurred while attempting to perform this command

The command does get executed, though. It only ignores the tag(s).

What I expected to happen was...:
The command gets executed succesfully with the text.

What actually happened was...:
The command executes but ingoring the tag(s) and displaying the error message above.

Steps to Reproduce:
1. Write a command in a command block or in the chat that contains the Text1, Text2, Text3 and/or Text4 tag(s) on a sign and execute it.
2. Notice the error message displaying and the sign stays empty.