If you have an experimental frenzy in hand and get copy cards added to your hand you are unable to exile the copies from your hand. You receive the confirmation asking if you want to exile the card however the card goes back to you hand after confirming you do indeed want to exile the card. Have tried with copy cards created by Lazav, the Multifarious, Thousand Year storm and Quasiduplicate. none of the copies can be exiled once Eperimental Frenzy is on the board.
//Edited Title - Tombstone