Sorry, I am new to meshlab, also. I just downloaded the other day and all I have been able to do is read some of the information from the site and from Wikipedia.
I know from other reading that somewhere along the way during transfers, this polygon problem will pile up on you. I think you were talking about coplanar faces. I took this to mean you have a bunch of superfluous edges subdividing faces. There are some render apps that do not tolerate triangles and others that do not tolerate quads. Frankly, I am bumfuzzled.
But, since this topic is started, you will almost certainly get more qualified advice.