Please attach a test case (Inkscape SVG) exposing the reported issue to allow further investigation (at first sight though this looks like a basic question of usage, outside the scope of a bug tracker).
<off-topic>Note also that Inkscape 0.48.4 is rather outdated - apart from the last bug fix release in the 0.48.x series (0.48.5), the current release is 0.91.</off-topic>
4 of the five groups in layer (Ebene) "Bilder" have the filter effect 'Light Eraser' applied (see menu 'Filters > Transparency utilities > Light eraser'). Inkscape does not do this by itself - the effect was at some point applied by the user (whether intentionally or accidentally by this user, or intentionally e.g. by the original author (if imported as clipart) we can't tell). To remove the undesired filter effects, select all affected groups, and apply menu 'Filters > Remove Filters'.
Note that for each selected group, the message in the status bar gives the user the hint that the selected object has a filter effect applied (so even if the effect originated from an externally authored drawing, the current user does have access to information about object attributes).
German translations of the referenced menu items:
1) Filter effect in use:
Filter > Transparenz-Werkzeuge > Helligkeits radierer
2) Command to remove filter effects:
Filter > Filter entfernen
Please attach a test case (Inkscape SVG) exposing the reported issue to allow further investigation (at first sight though this looks like a basic question of usage, outside the scope of a bug tracker).
<off-topic>Note also that Inkscape 0.48.4 is rather outdated - apart from the last bug fix release in the 0.48.x series (0.48.5), the current release is 0.91.</off-topic>