POST Data Problem

hey guys,

we experienced a problem.
We've an input field which looks like

Code:

<input type="text" name="sku[206300.076000][15721][0]" value="" />

after submitting the form with CI
the output is the following

PHP Code:

Array
(
    [sku] => Array
        (
            [0] => Array
                (
                    [15721] => Array
                        (
                            [0] => asdfasdf
                        )

                )

        )

) 


if i do this without CI it shows

PHP Code:

Array
(
    [sku] => Array
        (
            [206300.076000] => Array
                (
                    [15721] => Array
                        (
                            [0] => asdfasdf
                        )

                )

        )

) 


As you can see CI replaces the name containing a dot with a 0.

I see in the documentation "Filters the GET/POST/COOKIE array keys, permitting only alpha-numeric (and a few other) characters."
Can i add some additional characters which i need ?

As a background notice:
We have a B2B Shop System built on CI and our client hast shifted from an older MS Dynamics NAV to the new 2015 Version. Somehow they  support product numbers with dots and so on, and our cart module works with this numbers.