The group is an "encapsulation object". Ungrouping will delete that object, and with it, all glue points attached to the group will disappear.
I don't know it that's an exact description of the inner workings of Draw, but that's my conception of it, and all my experience on the matter supports that notion...
Apache OO 3.4.1/4.1.2/4.1.3, on Ms Windows 7/10 and Mac OS-X 10.8.5 and 10.11.
LibreOffice 188.8.131.52 on Mepis Antix MX 14