This is not a group for normal Excel features, but rather it is for
macros in the proramming language that is called Visual Basic for
Applications. However, look in the Menu > Tools > Edit. The "Allow
Drag and Drop" should be checked.
On my Excel 97, un-checking it takes away my little box on the lower
right of a selected cell  that allows the feature  you are talking
about. I figured this out by simply looking around a bit. When
something stops, don't forget to look in the preferences - in this
case called options.