Since addition of support for production restart in WS /api/system/restart, no change has been made to WS /api/system/status to indicate that the restart request has been taken into account and is ongoing.
In fact, at first, this was not an issue because the WS /api/system/status would almost instantly go into "DOWN" status.
Unfortunately, since the Compute Engine got its own JVM, the delay between the call to the /api/system/restart and the restart of the Web Server JVM has increased a lot (because the CE's JVM is shutdown first and only then is the WebServer). In the meantime, response from the WS /api/system/status is still "UP" which is confusing (and a problem for the UI, see
As a consequence, WS /api/system/restart should respond "RESTARTING" as soon as a call to /api/system/restart has been made. No error should be raised if /api/system/restart is called and status is already "RESTARTING".