Found an interesting article that details how a researcher's moral/cultural standards can influence their perspective and observations:

When science carries stigma​

Moral attitudes have long clouded scientific thinking about same-sex animal behavior. In 1906, naturalist Edmund Selous watched an all-male group of showy shorebirds called ruffs, including one inseparable pair, in the Netherlands. “They are constantly, so to say, mistaking one another for the female,” he later wrote. “Perverted sexuality is the real keynote.” A few years later, a researcher in Antarctica witnessed same-sex copulation among Adélie penguins but then coded his findings in Greek letters and didn’t publish them.
More recently, in 1986, butterfly scientist W.J. Tennent witnessed four male Mazarine blues vying for the attentions of another male in Morocco. He published his observations under the title “A note on the apparent lowering of moral standards in the Lepidoptera” and compared the courtship behavior to what he called the “horrific sexual offences” that humans commit.

Here we see same-sex behavior among non-human animals being brushed off as mistaken identity or ignored completely.

While the above is an example of researchers that had a bias against homosexuality, I don't think today's acceptance of homosexuality is immune from bias either. Researchers may try to impose their views on sexual orientation on non-human animal behavior.