Its Friday, and I don't think Ryuku-sama had his coffee yet, so I would suggest not reading his post if you can't watch the beginning of Bambi.
He makes an excellent point about understanding the mechanics that are happening there, and with bolster, tactical flashpoints, and over-leveled characters in Flashpoints, it can sometimes be frustrating to players who have been around a while to see inexperienced players simply ignore these mechanics, and plow through the fight.
In this instance, you can't ignore the mechanic (the shield), and you must interrupt the channel cast (I think its a channel in this case) of those mobs. Most likely you've played with other folks who understand these mechanics, and have simply taken care of it, without saying anything. This is a shame, but comes from hearing comments such as: "shut up, newb", "I've been playing since beta", etc. etc.