The actual environment I'm using
file ownership : root:hadoop # You are in hadoop group, you're NOT in root group
file permission : rw-rw-r--
file holding directory ownership : root:root
file holding directory permission : rwxr-xr-x

Reproducible: Always

Steps to Reproduce:
1. Open a file that is similar to the above "Details"
2. Modify it
3. Try to save the modifications
Actual Results:  
Shows a popup window : 
"The document could not be saved, as it was not possible to write to <file path>.

Check that you have write access to this file or that enough disk space is available."

Expected Results:  
Saves normally as there's no permission issue.

Vim editor saves successfully.  I doubt that Kate check's the permission beforehand using somewhat buggy mechanism instead of directly try to save the file.