Can't change title metadata of .mobi file?

Hello,

I am trying to change the title on a set of .mobi files I obtained from Oracle Corporation (freely available DB documentation). They are all titled "Oracle Documentation" but are on different topics. I'd like to title them by topic.
However, when I change the title via editing metadata in Calibre, it changes the file name on the computer, but the file still opens up with the title "Oracle Documentation" on Calibre, Kindle on PC, and via a Kindle Touch.

Specifically, I do the following:

(1) right click on doc in calibre, select "Edit metadata individually"
(2) change the title in the "Title" box; also click arrow to copy new title to "Title sort" box
(3) click 'OK'

Again, even after doing this, the title displayed by various readers is still set to the original.

This shouldn't be this hard, should it? What am I doing wrong?

I've searched the forum and haven't found any discussion of similar issues.

Any help greatly appreciated!! :help:

--David