That could be related to js script error which may be caused by incompatible/missing jquery / jqueryui or other dependencies of pqgrid thereby preventing or messing up the Ajax request. First of all, open up developer tools in IE by pressing f12 or from tools menu.
Click on start capturing in Net work tab.
Then navigate to Project Detail Page, look our for any errors on Console in developer tools.
Then perform any update in project fields and try to save the page using the project server save button.
Again look our for any errors on Console in developer tools.
Also check the logs under Network tab.