Lead Vocal dropouts when using VH!!

[entertain70]

Hi!
When I'm singing and want to use the VH everytime my lead vocal drops shortly out when I switch the Button ON. I've tried different things like changing volume-ratio of VH and lead vocal, used SUB Out for vocals, tried different presets... but nothing changed this unwanted effect. I can rember that I've had the same problem on my T5.
Anyone else having the same issue?
Thanks, Joe