Forgive me if im wrong but shift+D used to create a duplicate but if you moved the keyframes it would not affect the original objects keyframes, now you also have to unlink it after shift+d, whats the point when surely if you wanted a linked object you would use alt+d?
That is still the case.
By default, when you press shift D, object is duplicated and its animation data is duplicated.
Original object has an action and duplicate has a duplicated action with same keyframes.
Both actions can be tweaked individually.
If it is not the case, maybe, you modified User Preferences.
What is duplicated and what is not while pressing shift D is defined into Duplicate Data subpanel of Objects panel of Editing Tab.
By default, Action checkbox should be enabled.
Or you were confused by 2.8 UI.
In 2.79, you are forced to go into dopesheet to move keyframes.
But in 2.8, timeline displays a summary of all animation channels.
When you are in dopesheet, channels related to selected objects are visible.
When one object is selected, only its channels are modified.
But if several are selected, channels of all objects are visible. At that moment, tweaking keyframe in Summary line means tweaking keyframes of all channels for all selected objects.
So, you probably move a keyframe with a selection of multiple objects, in timeline.
If you only select one at a time, it should work as you expect.
Thanks for the reply. Its not creating a new action just the same action. I reloaded factory settings and it works like its supposed to and creates a duplicate action. I compared my settings to factory settings for editing and animation and they seem to be identical so the only thing i can think of is that an addon might be causing the behaviour or a setting in another menu.