False DateTime calculation using .plusMinutes?

I use this line in my rule

(now.withTimeAtStartOfDay.plusMinutes(1439)).toString

And I’m getting “2017-02-01T00:00:00.000+0100”, today is 2017-02-28!!

Am I missing something?

Stupid .Me, the code took another “way”, so the unexpected behaviour is caused somewhere else and I see MY error!
The posted line works as expected!
Sorry