I find that Avant and Orca behave exactly the same in this respect. I suspect that you have an IE setting or plugin that is manipulating new windows, hence why you are only seeing it occur in Avant.
Try the test buttons on this page
to check. If you have a specific URL to test then please provide it.
There is a maximise all windows option built into Avant and Orca. It is on the window management bar. Its default position is in the dropdown for that bar - but you can make it always visible with: View >> Customise Buttons... >> Other Buttons >> Maximise All