Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. Start 2 Confluence instances, at least one of them should be running on Windows
2. Do some changes related to plugin (for e.g. TeamCal) so it will save information to it's active objects table
3. Go to General Configuration -> Backup and Restore
4. Choose backup option
5. Generate site backup
6. On instance running on Windows go to General Configuration
7. Open Logging and Profiling and add Debug logs for com.atlassian.confluence.impl.backuprestore.restore.container.PluginDataReader
8. Go to Backup and Restore and choose restore option
9. Restore site from backup generated at step 5
10. Check data from TeamCal plugin

Expected Results

Active objects data is restored and there are log messages from 

com.atlassian.activeobjects.confluence.backup.LoggingBackupProgressMonitor about it:

WARN [confluence.backup.LoggingRestoreProgressMonitor] beginRestore Begin restoring Active Objects backup, adjust log level for com.atlassian.activeobjects.confluence.backup for more detailed logging.
...
WARN [confluence.backup.LoggingRestoreProgressMonitor] endRestore Completed restoring Active Objects Backup. 

Actual Results

Active objects aren't restored and there is a log message that we couldn't read plugin data:

[backuprestore.restore.container.PluginDataReader] readPluginData No plugin data for : com.atlassian.activeobjects.confluence.spi:activeObjectsBackupRestoreProvider                                                                                                             

Workaround

Use legacy site restore to restore active objects data.