A bisexual character’s attraction or interest in one gender is ignored/forgotten. Most of the time this indicates a character’s interest in people of a different gender is explicitly stated or written to be obvious, while their interest in people of the same gender is subtle or downplayed, but the reverse does exist.
Characters with an established heterosexual partner are especially prone to this, as the romantic and sexual nature of the heterosexual relationships are explicit, while any same-sex interests are downplayed or not shown on-screen.This can be caused by the writers wanting to include hints a character is gay or bi but with enough heterosexuality to appease straight audiences or network censors. Additional reading: Ambiguously Bi