Cannot permanently delete mails from trash in gmail account

When emails are deleted using default Mac OS X Mavericks mail.app, they move to the trash folder as expected and when I delete them from the trash folder, they dissapear as supposed. Unfortunatelly, after logging in to the gmail web-based version, the emails are still visible in trash folder. They are sort of hidden, because they are visible only in web-based version, not in any smtp client. Interesting is, that iPhone mail app deletes the mails correctly. This issue was tested on 3 computers (iMac 27" i5 late 2010, Macbook Pro Retina 15" i7 early 2013, Macbook Pro Retina 13" i5 late 2013), 3 user accounts, and 3 gmail accounts. Do you have any suggestions?

Yep. Agree, the best solution is to let my iPad/iPhone do it as they delete the trash correctly. Thx for this simple tip.