Hi, I have been pissed off by this problem a long time and assumed it was ATIís fault. Tonight I made one last effort before ordering a Nvidia graphics card. And I was successful.
I am running catalyst 9.8 using a Radeon 3850 and have had this re-size/maximize problem as long as long as I have used KDE4. To solve the problem I needed to modify a file in xorg-server. in the code directory it is called ./composite/compalloc.c. Here I commented out most of a function called compNewPixmap. Everything below these lines:
pPixmap->screen_x = x;
pPixmap->screen_y = y;
all the way down to (but not including) the last line:
After this I am running KDE4 with all desktop effects that I want and without any lag in resizing/maximizing.
I am running Gentoo, so I just updated the xorg-server source package file and put it back into the source repository, rebuilt the manifest and emerged it again. Voila!