Basically, it's not a bug. It's problem related with Gmail security requirements. If you want to use Gmail account as your e-mail account in nopCommerce you need to enable 3rd party softwares support in your Gmail. Please look at the steps below how to successfully configure Gmail email account in nopCommerce.
1. Log in to your Gmail.
2. Please enter https://accounts.google.com/DisplayUnlockCaptcha and allow access.
3. Please enter https://www.google.com/settings/security/lesssecureapps and allow access.
4. Login to your nopCommerce, then go to Configuration -> E-Mail Accounts and Add new or Edit existing account.
5. Now use below listed settings:
Email address: Your email
Email display name: your website name
Password: Password. (NOTE: If you are editing existing account, don't forget to click "Change password" button.)
Use default credentials: Unchecked.
6. Save changes.
7. That's all. You can send test e-mail, but everything will work.