'Incorrect' correct password

Sometimes (maybe every 2-4 month, i didn't log it) my Samsung Galaxy S4 with 5.0.1 does something strange:
When i want to unlock the phone it says "incorrect password" allthough i am 100% sure that i entered the correct pin. Re-entering the correct pin doesn't help - tried this till my phone said i used the wrong pin too often and i should stop now for some minutes.
When i reboot the phone the pin is accepted on the first try...
I did a very quick google search, but there are millions of posts in which people forgot their pin and want to unluck the phone without knowing it. Couldn't find (in a short time) a simular problem like mine.

Do you know what's going on here? Or have you even ever heard of something simular?

Could be a bug in the password app.

Don't laugh, I experienced the same issue with an Oukitel. More of that, when that appeared and I was able to login, I had a semi transparent green small ball on the screen. After some times, I noticed when connected on WiFi, that when it appeared, there was data sent...
Of course, I won't use that one anymore

An Schi said:

Do you know what's going on here? Or have you even ever heard of something simular?

Click to expand...

There are some issues reported about this behaviour (see Google). What ROM do you use? CM? Rooted? I had the S4, too but never any problems with it.

I don't use any mod - it is the custom Samsung rom. Never touched it.
You are probably right about google. But as i said in the first post, there are tons of missleading searchresults. Need to find 2-3 hours to dig through this...