IE7 Strict mode AxtiveX control arrow keys no longer work.

We have an intranet aspx page which loads an Activex control that is
essentially a treeview. We have been running in Quirks mode and the 4 arrow
keys can be used to navigate the tree just as in a Windows Form Treeview.

Now we have added a valid DOCTYPE (4.01 Strict) to the page and IE7 went
into Strict mode as it should. However, we can no longer navigate in the
ActiveX control using the arrow keys. They are just ignored. I found I could
navigate using alt up arrow and alt down arrow but the left and right arrows
still fail to function even with the alt key. Does anyone know why this has
changed and what we can do to get the old behavior back?