I don't think there is any one focus for stereotypes. I think the media treats lesbian relationships seriously. Look at the show on ABC FAMILY of all channels, the Fosters, with a married lesbian couple adopting and raising children and shown as good parents and role models.
It's actually my favorite topic and I have to disagree here. For every positive portrayal there is negative one. The usual way to create some drama in lesbian relationship is to make one of the women involved sleep with a man. Sometimes the writers have as much "respect" to not make the gay one do so (Last Tango in Halifax - where after her bi girlfriend cheated on with a man to get pregnant year ago recently the lesbian partner has been killed off shortly after them having a wedding), but oftentimes, the lesbian just suddenly finds herself craving sex with a man (last year in Waterloo Road, where lesbian was chased by a man who wanted to turn her, and then right after he opened emotionally himself to her they had passionate sex, or also from last year, EastEnders, where one lesbian slept with a man while being drunk, and her also lesbian partner did some non-showed "stuff" with a man to get pregnant few months later, or In the Club, where lesbian too had sex with a man to get pregnant).
Also just from last year in regard to non-commited lesbians, Dracula where lesbian slept with a man and it looked like she had the best time of her life (the creator himself admitted it enouraged homophobic myths and said that he and the writers intended for her to look traumatized, but during execution of episode something went wrong), Faking It although this one deserves a bit more explanation for another time, or Hell on Wheels, although in this case the character was never labelled which has been quickly used as defense.
There's also movie with Al Pacino, The Humbling, hitting theaters this year and it's story of a lesbian basically being turned into wifey of much older man.
Even the work that is generally considered positive for representation often plays with those tropes. In Pretty Little Liars, out lesbian character suddenly made out with a man and was "confused", there were provided two opposite explanations by different characters - one that she did it because he reminded her her dead girlfriend, another, because "sexuality is fluid". It seems it was pushed by producer (who's gay man BTW), because he was talking in interviews before the season started that she will fall for this "sweet, sexy guy".
Or another, Lost Girl, where they invented some crazy fantasy scenario just to make the lesbian character be showed having sex with a man without it actually happening. The showrunner even admitted that they did so because some male fans wanted to see it, and apparently thought they were so tactful and respectful because they didn't do it "for real".