Sign does not save I inputted

I can't input the sentence including '§1Blaze' anywhere into the birch sign. The entire sentence disappears or it displays as "#######". (screenshot is the latter)

Also I can't input the sentence including '§1<-§1B' anywhere into the birch sign. Same thing happens.

In the screenshot, notepad in the bottom right shows the sentence I inputted, and the result is shown as the center birch sign.

This happened in Realm server.