Weird submit value of calculation

Hello, even I know, that there is no free support for this plugin, I hope someone can help me.

I′m encountering a problem with calculation field, or with its value in summary.
Here is an example.
Calculation_1 is Field_1 * Field_2, in numbers e.g. 1000 x 100 = 100000. This value is ok and is displayed on screen, and also is in summary in e-mail confirmation.

Calculation_2 is Field_3 * Field_4, in numbers e.g. 100 x 9 = 900. This value is again ok (displayed on screen, in summary in e-mail confirmation).

Calculation_3 is Calculation_1 + Calculation_2 = 100900. This value is correctly displayed on screen, but in e-mail confirmation summary is 101.000.

So it means, that from some reason the value was divided by 1000 and rounded.

Does somebody have an idea, what is wrong? I′ve tried changing money formats, disable money formats etc. I just can′t understand, when the calculation in form is ok, why the value in summary is wrong.

Thanks so much, to anybody,
Tomas