Comment 34 for bug 774985

I think there are some misunderstanding in the offered workarounds above however the issue/bug is clear and still exists.

To replicate the issue :
After a fresh install, under configuration->sessions choose "Load last used session".
Open A.txt, close kate, reopen kate. Observe that A.txt is not opened.

I think Kate supports two use cases, one is working with sessions : you can save open load sessions etc... This mode is working fine.

Another use case is working without any session (or unnamed session if you prefer). This seems like it is the default mode. This issue is related to that. When you choose working without any session then you enjoy global recent files menu (as some users prefer) and you supposed to have a single session.

A workaround is create a session say MyFixedSession,
then update the kate.desktop file with

Exec=kate -b --s MyFixedSession %U

P.S. If you run "kate somefile.txt" from the terminal it will start a new session. So you might need to use "kate --s MyFixedSession somefile.txt"

best,