Certain characters turn the glowing text outline on signs gray

Steps to reproduce:

1. Place the sign.

2. Write/paste "秋" or "吧" (you can also add other letters).

3. Take the Glow Ink Sac and make the text glow.

Observed results:
The line containing "秋" or "吧" has a gray outline.

Expected results:
The line containing "秋" or "吧" will have a white outline.

Original description:
Create a map randomly, without open cheats and developer options. No mod added. As long as these words are displayed, this problem will occur, please fix the official.(Transported from MCPE-184834，became that's chinese)