Choose Type > Show Hidden Characters, then take another screenshot and post it here.
thank you very much, but Eugene Tyson has solved my problem.
Thank you all the same, i learnt that next time when i have a question, i should print a screen shot with hidden characters.
Thanks you Tyson, it's very helpful. It must be the problem when my german colleague compose the general paragraph style and checked the "balance ragged lines" box.
I simply uncheck it, it's normal again now.
I gotta learn more about what "Balance ragged lines" is. (sorry my first language is Chinese so it's a bit difficult reading english, especially all those apps including OS are in english.)
Thanks again and wish you Merry Christmas!