custom fields area in post section error

Please check this screen shots.

Here 1
Here 2

My custom fields area combo box gets out of screen, and makes me to scroll horizontally.

I checkd the items in the combo box, deleted corresponding rows in wp_postmeta table using phpmyadmin. Deleting the metadatas, however, the other meta datas come up iteratively. That implies the metadatas shown in combo box do not have distinguished character with other metadatas, i think.

Thanks in advance. ??