Flask Crit Chance Suffix

While crafting flasks for my mageblood, I noticed that the suffix "Increased critical strike chance during effect" wasn't increasing my tooltip crit chance for glacial cascade. From what I can see online, I thought that it would increase my crit chance for my spell. Does it not work like that? Or is the tooltip wrong?

POB seems to think it increases spell crit for me but I know POB can be weird sometimes.