No warning that private repository becomes public after fork

I forked a private repository from a client today. I was sure it would be kept private since "Private repository" was pre-selected and unchangeable. But then my fork was publicly visible without a further warning.

I suspect that it would have been kept private if I wouldn't of already had used my private repository on my free plan.

• it was not clear that forking a private repository would count as a private repo on my account
• there was no warning or indication that the repo would become public. The fact that "Private repository" was selected was very misleading.