TrinityCore/TrinityCore — comment on commit 5ea49613d24ad10b305891a39340155058e5a67e
File:  line 0
By Kline-:

DD spells will continue to cast if the target is out of LOS then fail with an error message after the cast time is finished. DD spells only check at the start and end of casting.

Again, from the WoWWiki page to channeling I linked (emphasis mine):

>For a **channeled spell, the LoS check is done before the spell is channeled**. So if you passed the check and you hit your target, your damage will be applied and **your target cannot run out of your LoS anymore** (apart from running out of range). This can be very handy against skilled players, as **your normally cast spells can easily be "dodged" (by running out of your LoS)**, whereas for channeled spells you just need to keep pressing the button until the animation appears and the damage will go through.