Duplicate tag created if tag name contains ampersand

[sillybean]

This is undoubtedly an edge case, but here's what happened:

1. I created a tag with a long name that contained an ampersand. Gave it a shorter slug than the one WP generated.

2. Tagged some posts.

3. While the server was running slow, the autocomplete never came up, and I tagged another post by cutting and pasting the tag name from another screen.

That resulted in a new tag being created with a longer WP-generated slug, instead of the post getting tagged with my older existing tag.

This happened a few times (the server in question is REALLY slow), and I finally realized that the only tags that were incorrectly duplicated were the ones with ampersands.

[dd32]

This might be caused by "Test & Slug" being stored as "Test & Slug" in the terms table.

However, There is another side to this story.

Create a tag as such:

Name: Some Tag
Slug: st

Attempt to create another tag as such:

Name: Some Tag
Slug: 

Result will be a second tag created with 'some-tag' as the slug, as the name is ignored in the comparison, its only checked to see if another term exists matching that slug (be it provided, or automatically generated)

That testing is done from the Manage -> Tags screen, but its most likely also the underlying cause of the Tag additions.

[dd32]

There is some issues with the Suggest and & due to & The search doesn't abide the same escaping. See #13992.

[aaronholbrook]

Cannot reproduce and dd32's steps to create a secondary tag with a missing tag no longer applies.