This has been a bug for at least a version or two: draw a shape, go to transform it in the Properties panel, and even though the "Maintain width and Height Properties" icon indicates "not constrained", adjusting one of the dimensions adjusts the other proportionally. This seems to happen only in a fresh file (perhaps fresh launch of Illustrator), and once I click and unclick the Constrain button once, it doesn't recur in that session.

https://www.dropbox.com/s/u0gqadn2lezzq7n/Constraint%20bug.mov?dl=0

So in the screen grab above, I draw a box freehand, then in the Properties panel, begin adjusting the height with my arrow keys. You can see the icon to the right indicating width and height are not locked together, but still, as I adjust the height, the width changes in proportion.

Note also that once I click that icon to specify "Constrain," then unclick it back again, now I can adjust the two parameters independently. And from then on in the file, the bug doesn't recur.

In investigating my own question from in the user forum (https://forums.adobe.com/message/10238447#) I discovered that there is a disconnect between the Transform panel that is embedded in the properties panel and the Transform panel that you access via the Window dropdown.

The free floating TRANSFORM panel you access from the Window dropdown works just like it always did... when I put my cursor in the X, Y, W or H and click an up or down arrow key it first rounds to the nearest .125" then increases or decreases .125" at a time (assuming the units are set to inches).
The Transform section embedded in the new PROPERTIES panel does NOT work properly. It only goes up and down in 1" increments.

I am using Illustrator 22.0.1, and I do not believe this has been addressed yet.

The new Properties panel has a fixed width. When it's in a tab group with panels that don't have a fixed width (eg. the Layers panel), the tab group exhibits different behaviours depending on whether the tab group is docked or free-floating.

When the tab group is free floating, switching between the tabs causes the panel to change width according to each tab's setting, which is what you would expect. Eg. Go to the Layers tab and make the panel very wide. Switch to the Properties tab and the panel auto-shrinks. Switch back to the Layers panel and the width auto-expands back to where you set it.

But when the tab group is docked to the side of the open document then no matter what width you set for a panel, the width auto-shrinks when the Properties panel is selected but doesn't auto-expand to it's previous width when you switch to a different tab. Eg. Start with the Layers panel and expand the width. Switch to the Properties tab and the panel auto-shrinks as expected. But switch back to the Layers tab and the panel does not auto-expand back to the previous width setting as it should, instead it stays at the Properties panel width (which is a useless width for most other panels)

This makes it very difficult to include the Properties panel in a tab group with panels of varying width, such as the Layers panel.

In 2018 AI CC, after using a group/clipping mask with text on the inside, you can not edit your text when you double click on the clipping group/mask directly. The Properties panel doesn't display the character settings. See my screenshot

So, to get around this, I have to cut the text out, paste on the main layer, edit it and then cut/paste it back inside my group/clipping mask.
Or, release the entire mask, make my edits then re-group/mask it afterwards. Or I have to open the separate character panel.

As opposed to the way it should. The only way the Property panel display the character settings is if you create/edit your text ONLY on the main layer.

just noticed something strange in the pulldown menu of the new Properties panel. The values for thickness are marked with a dot for decimals, while all the other panels use a comma.

In the picture you can see the pull down showing values with ".xx pt" while the stroke has a thickness of ",xx pt" (obtained through the Strokes panel)

This causes the 0.5pt selection in the Properties menu to make strokes with a 5 pt thickness, and NOT 0.5 pt.
(When I select the thickness through the regular Strokes panel it says 0,5 pt and ends up with 0,5 pt thickness)