iCal resizes on reopening after El Capitan on MBP

Since I upgraded to what I've found is a generally excellent El Capitan, whenever I open iCal on my MacBook Pro it opens resized to about half the size it was when closed down. I've tried to close it gently and forcibly but with the same results. Are my preference or plist files corrupted? It's very annoying to have to resize it every time I open it. Any ideas for a fix out there? thanks.