Nellie Bowles explains:

Horvath, who joined San Francisco-based GitHub in 2012, also founded its laudable Passion Projects series of women in tech talks to “surface and c elebrate the work of incredible women in our industry, as well as produce more female role models within the tech community.”

Nonetheless, GitHub has been embroiled in a series of diversity controversies, such as programmersadding racial and sexist slurs into their code. But with Passion Projects and hires like Horvath, GitHub CEO Tom Preston-Werner said he was trying to change that culture. The talks encouraged more women to join the company, and he said a quarter of the 60 new hires after launching Passion Projects were women. Horvath also said she’d noticed major changes at GitHub as more women were joining.

The shift in Horvath’s tone is problematic for GitHub, because she had been a long-time defender of GitHub. But even in a January interview with ReadWriteabout how progressive the company had become, she noted some lingering issues: “I recently got an email from a middle manager that began, ‘So Julie, how are the women at GitHub?’ I said, ‘You should ask them.’”

She clarified on Twitter that this is harassment not sexual harassment. 

She's raging against Github's culture of bullying and aggression:

http://pandawhale.com/post/39377/the-daily-dot-sexist-culture-and-harassment-drives-githubs-first-female-developer-to-quit