Bug? I'm not sure
Its not a bug but it is very annoying that you cant cancel the channel of life leech. Its gotten me killed a few times in TA because i wasnt able to switch to target a vile blossom in time. You can get around it by selecting a new target and using the fear to cancel but that can be a huge waste of the fear.
Like spoj said, you cant cancel out of life leech, so you are stuck on that one target until the channel ends.
Or press 4 to interrupt it.
That is indeed pretty annoying. You can interrupt it with any other skill tough (not just fear) and then retarget.
I only mentioned using the fear because the other 2 arent available from the start. Infact you are usually dead before they become available.