When in online mode, saving a document to the Sandbox causes the WAN bridge to attempt to also save the file to the repository.
Saving to the Sandbox occurs immediately. Saving to the repository takes more time than saving to the Sandbox. In the event that you issue additional local save actions before a background save to the repository completes, the system will skip the saves that are waiting to be processed, and only save the last version to the repository.
When a document is saved during a checkin to the repository, the save is always performed in foreground and Oxygen freezes until the save is complete, and the document is removed from the Sandbox.