Do you have a MIDIclock connected ? Try disconnecting all MIDI/USB cables (if any) and see if it makes a difference. Also, make sure MIDIclock in is not enabled on the MIDI system menu – if it is, it may overrule the Tap.
I really can't think of anything the unit would do which would have the results you describe, so am disinclined to think it is a fault. But, anything is possible – let's just rule out other things first.
