Resizing grouped objects result in one of the objects having a fixed line width. How can i stop this behavior?

Explanation: I have 6 objects. One of them is a rectangle. These 6 objects are grouped. The group is copied to an .cdr to use it for use in designing a banner.
For this banner i stretch the group  from the corner of the selection. Everything stretches to the desired sizes execept for one object. This object is a rectangle and outline width keeps after stretching the same 0,508 mm width as before stretching.
Help to solve this is very welcome.