something wrong with signs

Something about these letter in this specific order on a sign makes the text on the whole sign disappear.

Chuck'n'Larry's

 

It only happens if it's the first line of the sign.

 I did a little testing myself and noticed that it seems to be the letter k that is causing the problem. See screenshots. You can see the sign in the background is blank in 2 shots but the third it is working normally.