Text Fields add value insert at correct place

Hi All~
I found something strange.
When I added some addable filed I found the textbox didn't
insert at correct place.

I found the missing textbox in the upper column
when I drag the draggable icon.

After I dragged the textbox back to where it should be,
it could add the textbox at the correct column.

demo.vitalskm.com/template/km/Fl ... roblem.mov

this is the screen flow

So did anyone found this problem.
And this is the test link.
goo.gl/01LO7
user/pw>>admin/gss99

Thanks for any suggestion.

hello
what is your browser ?
did you desactived joomla cache and gzip compression ?
and desactived plugin for mootools ?
regards

I test with many browsers ex:Chrome,firefox,Opera,IE8
And I disable the gzip、cache、mootools update functions.

I have other item type also with text fields,but have no problem with adding text fields.

If I delete the fields,and adding new fields to the item type.
the problem not happen.

maybe a problem with name of field ...

I delete some problem fields before.
And I use the same field name to add theme,it worked well for a day..
After a day..It crash again (T(工)T)

I had rename all the fields.
but it still the same.
Is it work depend on fields' ID?

many thanks~!