Bug overview description.
When trying to use tag scripts to quickly remove an emoji-based tag, the tag gets replaced by a different tag with Chinese characters instead.

What part(s) of the site page(s) are affected?
Post index/search.

What is the expected behavior?
The emoji-based tag is supposed to be removed outright.

What actual behavior is given instead?
🤪🤪🤪 (the tag in question) was instead replaced with 浪浪浪.

Time of incident (if applicable).
5:57 AM UTC, August 19, 2019.

Can you reproduce the bug every time?
Yes. This happened four times in a row. (I was removing a made-up tag added to several posts by a vandalizing user.)

What steps did you take to replicate this bug?

• I searched for posts with 🤪🤪🤪 in them.
• I selected "Edit tag script" from the Mode drop-down list.
• I entered -🤪🤪🤪 in the prompt's text box and selected "OK" to enter "Apply tag script" mode with that tag script.
• I selected all the posts that had the tag to apply the script.
• Instead of just removing the 🤪🤪🤪 tag from each post, the script replaced it with 浪浪浪.

When I noticed what had happened, I had to manually edit each post to remove the new tag.

Errors or other messages returned (if any).
N/A.

The emoji and the Chinese character have related Unicode code points (U+1F92A vs. U+F92A), which suggests some bug related to string processing, probably an issue with characters outside of the BMP since they're identical in the lower 16 bits.