": //" in URLs is converted to Smileys - how can you fix it?

Hello Developers,

You have developed a passable Forum Tool and since today I use it under https://runbb.wpzweinull.ch/slim-skeleton. Unfortunately an issue with this and in the URLs/Links from : // is a smiley face.

These characters in a URL are converted to smileys. How can I fix the problem or smileys I would like to use in the forum nevertheless.

Thanks in advance.