"Left", "Right" and "Center" BB-Codes incorrect behavior

1. Go to "New Answer" screen
2. Add any text, consisting of more than 2 lines.
Example:
Center
right
center

3. Select the text, press "Center" BB-Code button.
4. Select the second line, press "Right" BB-Code button.
5. Press "Preview".
AR: the BB-Codes work incorrect (the lines are not aligned according to the BB-Codes chosen). (see attachment)
ER: All the lines are aligned strictly according to the BB-Codes chosen (the first one and the last one should be aligned on center, the second one should be aligned to the right).

The same problem occur on "New Topic" and "New PM" screens.