My installation has been working for some years now.
I upgraded mantis plugin from 0.25 to 0.26 yesterday.
Today I modified job and project/category shows me only "-".
As soon as I open an exisiting job I see values from xml config file for a short time and it switches to "-".

After upgrade I downgraded plugin back to 0.25 and it still the same.
I compared config files from "hudson.plugins.mantis.MantisProjectProperty" (using config backup plugin) and they are byte identical.

I did not modified mantis install the last months.
So I ran out of idea.

Tried to log something using logger "jenkins.plugins.mantis", but it is empty.

Any ideas?