Whu doesn't it?
Article 4, Section 3 of the Constitution " New states may be admitted by the Congress into this union; but no new states 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.
And then you say this?
Article IV says that Congress and the legislature of the stat must approve. The partition of Virginia was approved by a section of the Virginia legislature not participating in the rebellion and which was recognized as the legitimate representatives of the Commonwealth by Congress.
So a "section" of the Virginia legislature is all that is needed to secede or divide a state into another state - not the approval of the duly elected state legislature? That sounds like quite a stretch in my opinion when one only goes with a "section." But of course, it must be legal since we still have W. Virginia, right?