It looks like the type for InitialValue is set to float and the model appears to allow a string.
<xs:element name='InitialValue' type='DataItemNumericValueType' minOccurs='0' maxOccurs='1'>
<xs:annotation>
<xs:documentation>
starting value for a {{block(DataItem)}} as well as the value to be
set for the {{block(DataItem)}} after a reset event.
</xs:documentation>
</xs:annotation>
</xs:element>
<xs:simpleType name='DataItemNumericValueType'>
<xs:annotation>
<xs:documentation>
The constrained value for this data item
</xs:documentation>
</xs:annotation>
<xs:restriction base='xs:float'/>
</xs:simpleType>

If this is incorrect, then the below seemed to match the model and pass validation:
<xs:element name='InitialValue' type='DataItemValueType' minOccurs='0' maxOccurs='1'>
<xs:annotation>
<xs:documentation>
starting value for a {{block(DataItem)}} as well as the value to be
set for the {{block(DataItem)}} after a reset event.
</xs:documentation>
</xs:annotation>
</xs:element>
It looks like the type for InitialValue is set to float and the model appears to allow a string.
If this is incorrect, then the below seemed to match the model and pass validation: