XML validation failing in regex

We have our code deployed on 3 production servers. This issue described below occurs only on one of the servers.

Validation of XML fails on one of the production servers and the Error Listener points the problem to the element ptp saying -
"Validation error: /wls_domains/gtcjbb001/validRds2.xml:0: error: cvc-datatype-valid.1.1: string value '/shelf=28/slot=8/port=28' does not match pattern for type of ptp element in limsData_T in namespace urn:com.bt.tdinfra.qt200tests.broadband"

Follwing is the declaration of ptp element in xsd.
<xs:element name="ptp" nillable="false">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="/shelf=[0-9A-Za-z]/slot=[0-9A-Za-z]/port=[0-9A-Za-z]+"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

As per the xsd the XML looks fine. On further analysis it was found that the XML is marked invalid only when "slot" equals any number containing the digit "8". Rest all of the times on this server the XML is marked valid by XML Beans.

Please let us know the fix/workaround to this problem.