After speaking with someone on the post you started on the tsetmy.net forums, he/she suggested deleting the results from your results page. He/she suggested it may be a caching problem.
Before you do any of the following, because it will clear all of your results that you have up to this point, you may want to save what you have now by taking a picture of it. Judging by what you've posted, you already know how to do this. You can change the last option to "Show Max" before saving the picture so you can save all that you have already done.
Let me stress that I can't guarantee that this will work in fixing the problem, so it's up to you whether you want to clear your results up to now. When they are deleted, they are gone for good. Again, it's up to you whether to try this or not.
If you want to try it, do the following...
When you go to your results page, change the last option to "Show Max", if you haven't already done so. When I changed it to "Show Max" it showed me 121 results.
Then tick the open box to the left of the red X, which should fill all of the boxes with a check mark.
Then click on the red X...
This should clear out ALL of your results. You can then try a test again, using the 12MB manual test size, and see if it gives you a correct result instead of a skewed one like you had been getting.
Again, I can't guarantee that this will work, as it's only a suggestion. One thing is for sure, though, and that is that you aren't actually getting the 500MB+ speeds that the results have been showing.