Strange Behaviour strings and variables

[pymen]

Pycharm 4
self.change_translated_text(segment4, "translated_changed-3")

if i select 4 in variable segment4 and AND PRESS HOTKEY UP - it makes 5
but if i select 3 in text (string) "translated_changed-3 - AND PRESS HOTKEY UP - it makes 2
but if i select 3 in text (string) "translated_changed-3 - AND PRESS HOTKEY DOWN - it makes 4