I also had this problem and found the solution. When you check the continuous option you can go to the Number Tab and you'll see on the Expression table an entry called "Continuous X-axis" which enable you to choose the correct number format:
Yes, that is indeed a problem and I am not sure if I know a work around. May be re-open this thread by unmarking the correct answer and wait for another response. I am sure there might be a macro that you might be able to use, but I am just not aware of one to suggest you.