Serato saves midi mapping information in XML files. I found sections in theses files added more than once each time one saves the file. Example below. The user io tag contains now three sections. The first one is the original one the others got added each time I saved the file. If someone is interested I can make a more comprehensive bug report.

<control channel="13" event_type="Note On" control="0">
<userio event="click">
<slot_loop deck_set="Default" deck_id="0" slot_id="0">
<translation action_on="press" behaviour="explicit"/>
</slot_loop>
</userio>
<userio event="output">
<slot_loop deck_set="Default" deck_id="0" slot_id="0">
<translation action_on="any">
<alias name="Empty" value="0"/>
<alias name="Inactive" value="7"/>
<alias name="Active" value="16"/>
</translation>
</slot_loop>
<slot_loop deck_set="Default" deck_id="0" slot_id="0">
<translation action_on="any">
<alias name="Empty" value="0"/>
<alias name="Inactive" value="0"/>
<alias name="Active" value="0"/>
</translation>
</slot_loop>
<slot_loop deck_set="Default" deck_id="0" slot_id="0">
<translation action_on="any">
<alias name="Empty" value="0"/>
<alias name="Inactive" value="0"/>
<alias name="Active" value="0"/>
</translation>
</slot_loop>
</userio>
</control>