Antennas are designed to do well in a given range of frequencies. That does not mean that they have also been engineered to block out other frequencies.
So your VHF antennas are good at receiving VHF signals, and may be fair at receiving strong UHF signals.
As an aside, the Antennas Direct Clear Stream 5 was designed as a VHF antenna, but they noticed it does remarkably well with UHF in some applications. The manufacturer has gone so far as documenting it's UHF capability with the disclaimer that the UHF performance is 'out of band performance'.
http://www.antennasdirect.com/cmss_f...20with_uhf.pdf