It's unclear what's happening there.

Normally, a CK would not be masked, but it could be...and the handles (white dots) can be dragged to change mask size.

Going through the steps...
In the timeline, double-click the image with the green background. Or click MODIFY on the toolbar.
Click in the "enable ChromaKey" box.
Click the eye dropper that is just below that box, then move the mouse pointer to the green area of the image, and click.
Adjust the sliders for best clip, then click SAVE.

Add your background image on the next highest video layer and it will be seen in the area where the green screen has been keyed out.

I went through all those steps successfully and it looks fine in the PiP designer window but as soon as I save and play that part of the video the green screen clip shrinks to half the size vertically.....

Precisely where are you seeing this "422 mask scale height?"

Is "maintain aspect ratio" checked in the PIP designer? Scroll down the left side to reveal that setting.

What is the image aspect ratio? What is the project aspect ratio setting?

I re-did it following exactly the steps you outlined...the second I clicked save the image squashed again....

the Maintain aspect ratio box is ticked in the Object settings (under Properties)...scale says W .316 H 1.000

When I click on Mask tab Object Settings the Mask Scale says W 1.000 and H .422....not sure what this means but it seems to reflect the size dimension of the image I have green screened. It does not allow me to change this W or H setting though.

Quote: I re-did it following exactly the steps you outlined...the second I clicked save the image squashed again...

I see no "object properties" here, but that's in PD11. Perhaps there has been an enhancement in PD13.

But I do see an X - the top left choice under MASKS. Chosing that would mean NO masking. Is that your choice?

Can you attach a small image of the screen that displays the object properties?

https://forum.cyberlink.com/forum/posts/downloadAttach/18248.page

I have done some screen images....how do I attach/send them to you?
Can I email them ?

Share them with forum members, many of whom are more knowledgeable than I...

Click the ATTACH button, locate the files and click them individually, to upload.