Incorrect unicode chars handling in custom BBCode

Unicode chars are displayed incorrectly when used within HTML elements in custom BBCode HTML replacement.

Example to reproduce:
1) Create custom bbcode like:
BBCode usage - [test]

{TEXT}[/test]
HTML replacement - <input type=button value="Кнопка!" /> {TEXT}

(here the text "Кнопка!" is the Russian for "Button!")

2) try using it like [test]Тест[/test] (Тест is Test in Russian).

You'll get the button text like Кнопка!
See the screenshot.