Aha! Finally figured out something else that's been driving me nuts:

turns out the canned new "backup directory" dialog put its "back" and
"next" buttons at a different relative horizontal position than all the
other canned dialogs.  This explains why you had to keep moving the
mouse around if you wanted to do a straight all-default install -- the
Next button kept moving around.  Now the back/next buttons are in exactly
the same place on all dialogs, and you can click straight thru to the end.

PCbuild/python20.wse

@@ -416,7 +416,7 @@ item: Custom Dialog Set
     Font Name=Helv
     Font Size=8
     item: Push Button
-      Rectangle=172 185 214 199
+      Rectangle=150 185 192 199
       Variable=DIRECTION
       Value=N
       Create Flags=01010000000000010000000000000001
@@ -432,7 +432,7 @@ item: Custom Dialog Set
       Text Swedish=&Nsta >
     end
     item: Push Button
-      Rectangle=130 185 172 199
+      Rectangle=105 185 147 199
       Variable=DIRECTION
       Value=B
       Create Flags=01010000000000010000000000000000