In Elements 8.0.4 Win 8 I see the same problem. “Create new audio file window”, the window isn’t created. Does seem to be a problem there. But “Add to focused track of montage” seems to work, and creates a new montage if there isn’t one.
Re: the stereo file, I don’t know why Wavelab 5 would make left and right channels in a stereo file if the input is a single channel mono signal, unless you were feeding it in equally to both channels. Wavelab 6 and 8 don’t have an option to route one channel equally into 2 channels during record afaik.
I think one solution is probably to set the record file parameters to mono instead of stereo, making a mono file, and then if you need a stereo file for iTunes or something, render the mono file to a stereo file.