Isabel Ordaz left the show at the beginning of season 2 to work in theatre. When she returned for season 5, it originally a one-year contract, but the writers/producers enjoyed working with her again so much that offered her a renewal. She agreed as long as she could continue to do theatre, which explains her absences in seasons 6 through 9, but after season 9, she decided it was time to retire the character.
Antonia San Juan left the series after two seasons because she asked for a raise and her demand was denied. She would later return, but only for one more season.
Luis Miguel Seguí (Leo) and Antonia San Juan (Estela) were a couple in real life during the making of the show.
According to co-creator Laura Caballero, the opening credits weren't use since season 3 because it was expensive to create new cartoons every year (many actors left and arrived the series on season 1, 2 and 3) so they just displayed the cast names.
According to Antonia San Juan, co-creator Laura Caballero wrote the role of Estela Reynolds specifically for her.