Using Flame Burst on enemies frozen with Ice Spear will cause a bug. The monster will remain frozen but the one that casted Ice Spear will be attacked by it. This bug is known as "astal body bug" in many other foreign servers.
It's only today that I fully understand what this really meant. However, this description is quite flawed and doesn't explain the full story.
Flame burst alters the nature of Ice Spear. Ice spear normally freezes monsters such that they cannot move. The trouble with using flame burst is that it will cause monsters within a certain range (estimated to be the same range of effect as magical music) that has been frozen by ice spear to have the no-movement effect nullified. Therefore, you will see the monster being frozen, but in actual fact the monster is moving and then the person casting Ice Spear will get attacked by it. This is what the part "The monster will remain frozen but the one that casted Ice Spear will be attacked by it." and "astal body" really means.
The thing about the wiki description being wrong is this part: "Using Flame Burst on enemies frozen with Ice Spear will cause a bug." This is incorrect. It should be "Using flame burst on enemies within a certain range on any enemy (especially monsters not attacked by Ice Spear) will cause a bug on monsters attacked by Ice Spear." Thing is, if you use Flame burst on an enemy that is frozen with Ice Spear, it will still be "knocked back" by flame burst effect even though the no-movement by Ice Spear effect is nullified, so nobody will get attacked by it.
To give an illustration of this, we used two bears for testing, and I will call them Bear A and Bear B. My friend used icebolt at Bear A, and then froze it with Ice Spear. At the same time, I use flame burst on Bear B. This (flame burst) causes the no-movement effect of Ice Spear to be nullified and therefore my friend gets attacked by a ghost of Bear A even though it appears to be frozen.
We took another bear, Bear C, where she ice-speared it first and then I flame burst it. We received no signs of attacks from the bear.
The effect of this bug means that Ice Spear and Flame Burst in party situation is a very big no, especially if you are not going to flame burst the monsters that are ice-speared, and that's quite a serious bug since common sense tells you it should not be this way. Why would you get attacked by a ghost of a bear when the bear is supposed to be frozen?
I really hope they do fix it but I do wonder if there is enough awareness of this bug to begin with since I have heard hardly anything about this.