This is a known issue and it applies to many/all of our sis files but we will try to ensure the backup support from now on.
A workaround for this problem is to add the appropriate registration file yourself, from your own package by adding the following line to the PKG next to the one that embedds the sis:
where UID3 in in your case 10207bd2 and the *.xml file is the standard system backup:
; embed my_sis_file.sisx
; fix backup support for my_sis_file.sisx
"BinaryBackup.xml" - "!:\private\10202D56\import\packages\UID3UID3\backup_registration.xml"
Details about how this works in SDK's documentation and in TSS001073 - Backup of add-on DLLs
<?xml version="1.0" standalone="yes" ?>