Issue with Custom DateTime Type Field on Page in SharePoint 2013

We faced a weird issue in our project. We have issue regarding Datetime field. We couldn’t find exact root cause but since it took lots of time to resolve so sharing.
 
We have SharePoint 2013 farm solution. We have custom DateTime type column is added in our custom content type and content type is associated with our custom page layout. This DateTime field is required field.
 
Content editor has created the page using our custom page layout but when he tried to save / publish the page, error dialog box with following error is appearing
 
 “The file Test.aspx has been modified by <User> on <Date>”
 
Even though not any other user has been modifying the page. On above error dialog when we pressing “OK” button and save it again following error is appearing

  

We investigated a lot but no luck. Only solution which we found is that making the DateTime field optional. We did this change and it started working without any problem