Problems installing with the new interface

Since the new interface, I frequently have trouble installing games (Like Simon the sorcerer, or Fallout NV). I find this bug after cancelling the installation once and trying again:

When starting the installation, I got the bit where it asks to review the files needed for the installation and press continue, but I literally don’t have a continue button: All I can press is “Cache” (does nothing, can’t use it to select a local installer), and Cancel, which… well, cancels the install.