This would be because the space between the actual roman numeral and the hanging indent where the line of text begins is too close for the III. so it moves the text across so that the III. and the word are not overlapping.


To fix this I would suggest you either:
1) Select the numbered style, go to Format > Bullets and Numbering
2) Click Customise
3) Change the Number Position to Right and click OK
4) If this doesn't help go back into Format > Bullets and Numbering > Customise
5) Increase the setting for Text position for Tab space after and Indent at
6) Increase the setting by 0.2-0.4 cm and then press OK
7) Your numbered list should be aligned now

Let me know how you go.