After Icy turned Mirta into a pumpkin in Episode 14, Flora was able to remove the spell only by Season 1 finale. All other attempts before that were unsuccessful, which the Winx considered to be the result of Icy's very strong magic. However, the answer could have been hidden all this time... in the moon! (Aisha's Guardian of Sirenix will be like "Duh!" right now).

In Cinelume, at the very beginning of the episode, Mirta answered Griffin's question this way:

>On the first night of the full moon we shouldn't cast spells of transformation because light rays from the moon can create negative interference which could cause unwanted and permanent changes.

And in 4Kids, when Sky plans to infiltrate the Cloud Tower, Brandon warns him by saying this:

>It's a full moon; witches are particularly strong during a full moon. Their power's can sometimes double in strength.

Sky and Bloom sneaked into the Cloud Tower exactly on the first night of the full moon (this was even emphasized by the shot at the end of the scene) and Mirta was turned into a pumpkin the very next day. All this means that Flora couldn't remove the spell primarily because of the influence of the moon, which made the transformation unstable in Cinelume and powered up Icy in 4Kids.



Pumpkin Mirta and how the moon is related to her transformation.