Not psychic, hehe. I just decided to fully compile it myself and bumped into that error.
As for updating, I think 0.4.4 was the end of that branch, no? There won't be more upgrades to that version. The main development branch now is KeePassX 2.X and you won't need to compile for that, because as you know, it's what Ubuntu-MATE is already offering through the repositories. 0.4.4 is however a very stable version. It can serve you for years.
One final note:
I noticed the makefile doesn't do a standard installation. It should create a folder for you inside $HOME/bin. Instead it considers that the root folder for the installation. So you end up with a $HOME/bin/bin and a $HOME/bin/share folder. That is ugly!
Since you can already fully compile it, I advise you to delete $HOME/bin/bin and $HOME/bin/share and start over. Only this time, you are going to give it the folder name, like so:
First clean all the object files that were created during the build. So, trom inside Downloads/keepass:
$ make clean
Then build again, time time giving it the folder name (manually create it first):
$ qmake-qt4 PREFIX=$HOME/bin/keepass/
$ make install
And this time it will be neatly installed into ~/bin/keepass
Oh, and don't forget to mark the thread as solved, so that any future reader with a similar problem, knows there is a solution.