1. Insert a table into Writer document.
2. Select some cells (maybe whole table)
3. Look at Insert->Caption... menu
=> it is greyed out.
4. Deselect the table, and put cursor into a cell. Or even type some characters in the cell, and select them.
5. Look at Insert->Caption... menu
=> it is enabled, as expected.
It doesn't seem right that #3 is disabled: why would this selection mode contradict the idea of inserting of a caption for the selected object? How being inside a single cell of a table is more appropriate for this task?
Fully agree with the bug, no need for UX input.