Imagefield: Image lost when hitting the "return" key

There is a node type containing an imagefield (multiple allowed, see attached image 1) and an ordinary text field (attached image 2, label "Freigabe").
When hitting "return" after editing the content of the text field (see attached image 1+2) the form is re-displayed. The text field shows the new content (image 3) - but the image field is empty (image 4).
But the DB still refers the image and image files still exist at this time.

mysql> select * from files where filepath like '%KStA-20090810-nr183-s32.gif';
+-------+-----+-----------------------------+-----------------------------------+-----------+----------+--------+-----------+
| fid   | uid | filename                    | filepath                          | filemime  | filesize | status | timestamp |
+-------+-----+-----------------------------+-----------------------------------+-----------+----------+--------+-----------+
| 12926 |   4 | KStA-20090810-nr183-s32.gif | files/KStA-20090810-nr183-s32.gif | image/gif |    76909 |      1 |         0 |
+-------+-----+-----------------------------+-----------------------------------+-----------+----------+--------+-----------+
1 row in set (0.03 sec)

find files -name "KStA-20090810*"
imagecache/scale_medium/KStA-20090810-nr183-s32.gif
imagecache/scale_thumbnail/KStA-20090810-nr183-s32.gif
KStA-20090810-nr183-s32.gif

After saving the node the image including all uploaded image files is completely deleted.

mysql> select * from files where filepath like '%KStA-20090810-nr183-s32.gif';
Empty set (0.03 sec)

CCK-version: 6.x-2.9
Download method: private