Strict mode and ActiveX control key mapping changed

I have an intranet aspx page that hosts an ActiveX control. The control is
essentially a treeview. We have been running in Quirks mode for years and can
use the up, down, left, right arrow keys to navigate the tree just like a
Windows Forms Treeview.

Now we are converting our site to a valid DOCTYPE which of course puts IE7
in Strict mode. This for some reason affects the key mapping in the ActiveX
control. The arrow keys no longer work. I discovered I could use alt down or
alt up but I cannot get the left or right arrow keys to work at all. Does
anyone have any info on why this has changed and what we can do to get the
arrow keys to work as before? Or just to get the left and right arrow keys
working with the alt key as up and down do.
--
Pete