"New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress." (Emphasis mine.)
The partition of Virginia was approved by a body of the Virginia legislature loyal to the U.S. and not involved in the rebellion. Their vote to split was approved by Congress. The requirements of the Fifth Amendment was met.
You mean to tell me that Lincoln's government ignored the clear wording an intent of a constitutional article?
I'm Shocked! Shocked! I tell you!