Another bug? When the floating panel is on the right, double clicking should push it out to the left

After testing your exact situation I understand what you mean.

As @Robert at ID-Tasker already said, that's because your panel group is not docked. Make sure to dock it, that is move it so that it "magnetically sticks" to the right edge of the monitor. Then it will expand to the left on double-click.

After testing this, I do see that it can be annoying that InDesign can expand the panel beyond the monitor edge unless it's docked. In an ideal world, InDesign should detect the monitor edge and expand the panel accordingly (that's how menus already behave after all). As Robert also mentioned, second monitor considerations can also affect this behavior (of which I know nothing).

@dublove

(3) is docked - (1) & (2) are just close the the right edge of the monitor. 

InDesign is not checking if it's your only monitor or you have another one connected. 

What OS? What version of InDesign?

It works for me no problems.

Try resetting your preferences:

Windows: Start InDesign, and then press Shift+Ctrl+Alt. Click Yes when asked if you want to delete preference files.
macOS: While pressing Shift+Option+Command+Control, start InDesign. Click Yes when asked if you want to delete preference files.
A dialog will appear asking to delete the InDesign Preferences, select 'Yes' on this dialog.
Further info and instructions here if needed:
https://helpx.adobe.com/in/indesign/kb/indesign-preferences-support-file-locations.html