UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.101 Safari/537.36

Example URL:

Steps to reproduce the problem:
Intermittent, occurs 2 out of 4 times. goes away on refreshing once or twice.

1. use regex ^([\w\.\-_]+)?\w+@[\w-_]+(\.\w+){1,}$ for email validation
2. chrome version 53 won't accept it
3. gives error
Pattern attribute value ^([\w\.\-_]+)?\w+@[\w-_]+(\.\w+){1,}$ is not a valid regular expression: Uncaught SyntaxError: Invalid regular expression: /^([\w\.\-_]+)?\w+@[\w-_]+(\.\w+){1,}$/: Invalid character class.

What is the expected behavior?
regex should have worked/been accepted by the browser.

What went wrong?
Its i giving error and stopping to proceed next.
Intermittent, occurs 2 out of 4 times. goes away on refreshing once or twice.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? Yes all many versions before 53, it worked on 52.....

Does this work in other browsers? Yes 

Chrome version: 53.0.2785.101  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 22.0 r0