[TYPO3-commerce] Strange behaviour of dropdownfields (Typo 4.2.6, Commerce 0.9.8)

[Chris Bernhard]

Good morning dear list,

im offering articles like this in my online store:

T-Shirt / Size S / Color: Red
T-Shirt / Size M / Color: Red
T-Shirt / Size M / Color: Black

I changed the following line in class.tx_commerce_pi1.php
to remove the ALL Option.

(ca. line no. 559)

$attCode.= '<select 
onchange="document.getElementById(\'attList_'.$prod->get_uid().'_changed\').value 
= 
'.$attribute_uid.';document.getElementById(\'attList_'.$prod->get_uid().'\').submit();" 
name="'.$this->prefixId.'[attsel_'.$attribute_uid.']" 
'.$this->conf['selectAttributesParams'].'><option 
value="">'.$this->pi_getLL('all_options','all',1).'</option>'."\n";

$attCode.= '<select 
onchange="document.getElementById(\'attList_'.$prod->get_uid().'_changed\').value 
= 
'.$attribute_uid.';document.getElementById(\'attList_'.$prod->get_uid().'\').submit();" 
name="'.$this->prefixId.'[attsel_'.$attribute_uid.']" 
'.$this->conf['selectAttributesParams'].'>'."\n";
										
Now, if im loading the article detailview site, in the dropdownbox all
colors appearing, but if im right, it has to show in the Size Dropdown:

S + M

Color Dropdown: only red.

The right behaviour should be, that black appears only if im changing 
the size dropdown to size M.

And the next problem is, after changing to M, the S Attribute disappears 
from the dropdown.

Is there an workaround for this problem?

Many thanks in advantage and best regards,

Chris