It’s hard to really say, but I’d still say that channelled skills are intended to have this downside.
Check here: http://blog.treeofsavior.com/en/?p=243
Q) I saw Dievdirbys carving a sculpture in the game, but it looked vulnerable since it was surrounded by monsters. Does carving get cancelled if Dievdirbys get attacked by monsters?
A) Yes. Carving will be cancelled if it gets attacked by monsters. Therefore, in order to succeed carving you need to receive help from your party members or ‘Safety Zone’ which is a basic skill of Cleric class can protect Dievdirbys while it is carving a sculpture.
Skills which have a charge bar are either charge cast or channeled cast skills. A large majority of skills are of the ‘charge cast’ type, which means when charging they don’t go on cooldown until the charge is released and the skill is used. However, there’s a few which are of the ‘channelled cast’ type, meaning their cooldown activates instantly and are cast instantly, but require a charge time to go through.
Now from their dev blog, it seems the current method we have with channelled cast skills were intended. But, we have had skills like this with Super Armor before (i.e. Possession, Bwa Kayiman have had super armor whilst casting). Though it’s really tough to say if it is indeed a bug or an intended nerf.
The fact of the matter though is that it’s still the same even in the kTest server and this most likely would have been reported as such if it was indeed a bug.
And their intended solution for this is for you to use ‘Safety Zone’, especially as a lot of these types of skills are present on Cleric classes.
But we really can’t say unless IMC themselves mention that it’s a bug or intended.