That would be odd that mysql workbench would be adding the extra characters. Generally I use phpMyAdmin to create custom user meta while testing and have not experience that issue. If you have that tool in your web host control panel, give it a try to see if the results are the same.
It is possible another plugin or the theme is hooking into the user meta calls and introducing those extra characters… that get much more tricky to track down it is the cause.
Glad I could help!
If you have a moment, I would truly appreciate a review as they really do make a difference.
Thanks in advance for your time!