Build : 1.5.0-19 b02 LU
OS : Solaris
Hardware: any
Test spec : http://sqeweb.sfbay/deployment1/SQE/testing/ServiceTag/ServiceTagTestSpec.html

SUNWj5rt package is installed. When 64-bit package SUNWj5rtx is installed upon it, ST entry created as expected (see 6809906). But when it is removed, SUNWj5rtx entry is also removed as expected. But SUNWj5rt (32-bit) entry is somehow modified. New instance_urn is set to it (instance_urn is also modified in <JRE>/lib/servicetag/servicetag). And "source" tag is modified from SUNWj5rt to SUNWj5rtx value.
  

//SUNWj5rt ST entry, before SUNWj5rtx installation.
bash-3.00# cat /usr/jdk/jdk1.5.0_19/jre/lib/servicetag/servicetag
urn:st:529f056d-0e7f-41ab-a7f0-4bc5488c9549
bash-3.00# stclient -g -i urn:st:529f056d-0e7f-41ab-a7f0-4bc5488c9549
instance_urn=urn:st:529f056d-0e7f-41ab-a7f0-4bc5488c9549
product_name=J2SE 5.0 Development Kit
product_version=1.5.0_19
product_urn=urn:uuid:d5bed446-05f2-42ed-ba0a-153105a52413
product_parent_urn=urn:uuid:f3c20172-557a-11d7-93d0-d6a41ea318df
product_parent=Java 2 Platform, Standard Edition 5.0
product_defined_inst_id=id=1.5.0_19-b02 sparc,dir=/usr/jdk/instances/jdk1.5.0/jre
product_vendor=Sun Microsystems
platform_arch=sparc
timestamp=2009-05-08 12:21:43 GMT
container=global
source=SUNWj5rt
installer_uid=0

//Install and then uninstall SUNWj5rtx.
bash-3.00# stclient -g -i urn:st:529f056d-0e7f-41ab-a7f0-4bc5488c9549
Record not found
bash-3.00# cat /usr/jdk/jdk1.5.0_19/jre/lib/servicetag/servicetag
urn:st:a4051d82-b73c-4ed5-a0f0-e43c62ef0720
bash-3.00# stclient -g -i urn:st:a4051d82-b73c-4ed5-a0f0-e43c62ef0720
instance_urn=urn:st:a4051d82-b73c-4ed5-a0f0-e43c62ef0720
product_name=J2SE 5.0 Development Kit
product_version=1.5.0_19
product_urn=urn:uuid:d5bed446-05f2-42ed-ba0a-153105a52413
product_parent_urn=urn:uuid:f3c20172-557a-11d7-93d0-d6a41ea318df
product_parent=Java 2 Platform, Standard Edition 5.0
product_defined_inst_id=id=1.5.0_19-b02 sparc,dir=/usr/jdk/instances/jdk1.5.0/jre
product_vendor=Sun Microsystems
platform_arch=sparc
timestamp=2009-05-08 12:27:14 GMT
container=global
source=SUNWj5rtx
installer_uid=0

Issue is NOT reproducible with JDK 6u10. In JDK 6u10, SUNWj6rt instance_urn remains the same after installation and uninstallation of SUNWj6rtx, and ST entry also remains the same ("source" tag).