Tags Being Removed or Randomly Added When < Symbol Is Used

Expected behavior

I expected to be able to use symbols like < in tags for my posts.

Actual behavior

I'm seeing some strange behaviour when I include < in my tags. In all cases, the tag with < in it is removed by the app after saving my changes. In some cases, other tags have been added seemingly at random.

For example, you'll see I've added a <3 to my tags in this screenshot:

After saving the above changes and returning to the Post Settings screen, I saw that not only was <3 removed, but testing was also removed and three other tags had been added:

Steps to reproduce the behavior

1. Navigate to post editor and go through the steps to add new tags from the Post Settings screen.
2. Include any tag that has a < symbol and save the changes.
3. Navigate away from the Post Settings screen and then return to it.

Tested on Pixel, Android alpha-144

Possibly relevant past issues with numeric tags being removed from the app: https://github.com/wordpress-mobile/WordPress-Android/issues/8008

This was raised by a user in 1693771-zen who notes that they often see tags randomly disappearing from the app. The only reliable way I was able to reproduce the problem was when using tags with a < symbol, but there may be a wider problem here.

The user is locked into version 10.9.3 of the app as they're on Android 4.4.2.

Reproduce the issue from the post editor's Post Settings screen on Android using a tag containing <, then follow the save and reload behavior described in the report. Done means tags containing < persist after saving and returning to Post Settings, without unrelated tags disappearing or being added.