Error 500 after attempt to create article with special symbols in tag

How to reproduce:

1. login and click on Write Article button
2. enter some data into title and content
3. enter data with special symbols, for example <test>
4. " Tag <test> should not contain special characters " error appears, 400 http-response (screenshot)
5. remove special symbols from tag and click on Write article again

Actual result: nothing happends, error appears in about a minute http://screencast.com/t/t3kUrtySH
Expected result: article with tag creates

Note: article wil be created if you remove tag on the last step