The next patch. It didn't make it in time for the Monday patch just released, but all the other issues reported have been addressed I think. If you don't want to wait, open your Spell xml file in your favourite text editor - default place for this file is:
C:\Program Files\Steam\SteamApps\common\FE Legendary Heroes\data\English\DLC04_Spells.xml
if Steam is installed in the default spot, otherwise start from the SteamApps subdirectory of the Steam folder wherever Steam has been installed. Search for "Morrigan" then for the Morrigan's Call spell add the line mentioned in Reply #5 of this thread to anywhere in the Spell definition except between the GameModifier tags. Save the changes. Then start a new game (all XML data from the main, mods and other directories are saved and become fixed when you start a new game).