Edit - And we have yet another correct answer. I found a source saying that Crittenden accepted a Confederate commission on March 16, 1861, but did not resign his US commission until June 10.
Amazing how many guys were doing this sort of thing.
This, however, is not a correct answer. It was nothing more than a wild guess on my part, based on having watched a DVD of the Hatfields and McCoys and noting the mention of Buckner as the governor of Kentucky during the feud.
Alfred Thomas Archmedes Torbert held simultaneous commissions in both the USA and CSA armies. He graduated from USMA in 1855 and was commisssioned in the 2nd US Infantry Regiment. On March 16, 1861 he was appointed a 1st Lt in the CSA but refused the appointment, remaining a Lt in the USA. He ended his Army career as a brevet MGEN.