Undo-ing major changes adds considerable complexity to the software. It is not surprising you cannot UnDo a deletion.
Even if it worked before, it is entirely possible that rather than fix complex bugs, the design team decided to remove the UnDo of a deletion to reduce complexity and ease maintenance nightmares.
You may find the Cut of an object to the clipboard has better undo support than a delete.
As leroydouglas suggested, you can get there by reverting to the last-saved version.
-------
You are welcome to "Contact Support" and voice your complaints to them, but we are discovering that in some cases, their response is to revise the documentation (to indicate the feature is not supported) rather than revising the software. "It is no longer a bug if it works as documented."