COMSOL possible bug when running simulation

Hi all,
I have experienced some weird behavior of COMSOL. Basically, I have been running several simulations without getting the expected results, and then at some point (without any particular change in the settings) I have finally got the "right" results. This has happened several times in different configurations. I suspect this could be related to some hidden\missing parameter initialization or a bug.
Has anyone experienced similar problems?
Thanks in advance.

What kind of simulation are you running in COMSOL? They have many different types of solvers in the package.

--Max

I am running simulations with the in plane waves (TE or TM) electromagnetics module.
I am trying to reproduce some results published in literature about cloaking.