Steps to reproduce the issue

1) Login into joomla.
2) Edit any joomla category (content->category manager->select any category->edit).
3) Open same joomla in different browser.
4) Login with differnt user (not the same one).
5) Now you can see the lock on the already opened category.
If you trying to edit it you can not edit it, that is correct.
6) select that category and press check in button (check in the catefory).
7) Now you can edit that category (edit it and try to save your changes).
8) At the same time in same joomla but in another browser, second user can also able to save the same category, which has been saved by the frist uesr in other browser.

you can also watch this issue's video explanation at this link: http://youtu.be/udlk-ob6Fhk

Is it really a bug in joomla.
please correct me if i am doing any thing wrong in my above steps.

Expected result

After checked in the category both the user can edit and save the same category.

Actual result

joomla should prevent the second user to save the same category with out refreshing the page.

System information (as much as possible)

Joomla! Version : Joomla! 3.3.3 Stable [ Ember ] 25-July-2014 13:00 GMT
PHP Version : 5.3.10-1ubuntu3.13

Additional comments

Note!
I have followed this steps in joomla 1.5, joomla 2.5 too and found the same bug.