Have a static field with a label containing "+" character
<formElement type="sb" ID="F1685" rank="4" required="0">
<name>status</name>
<label><![CDATA[Status]]></label>
<bind type="static" is_rank_alpha="0">
<items>
<item ID="V2064" label="Code review" is_hidden="0"/>
<item ID="V2065" label="Code review+" is_hidden="0"/>
</items>
<default_values>
<value REF="V2064"/>
</default_values>
</bind>
</formElement>
Export tracker structure and then try to import it in an other projet, you shoul not have a validation error