Can sometimes log in without passphrase

[acurious]

Signed up without using an email. Added passphrase to my primary login seedphrase. To my surprise, I was occasionally able to log in without passphrase, too. What's even more curious is that I could see the same wallet with same addresses as if I was logged in with passphrase. Uninstalled, tried to recover from seedphrase+passphrase. Could not log in anymore since the app could not find the corresponding user from servers.