Hi Ivan,
Thanks for the heads up on these. The Zero Span center frequency resets to 1 GHz each time you start the program. If you click the zero-span button on the control panel, it will use the current center frequency as the new center frequency for zero-span. Also, if you use the file menu to get to zero-span, it will use the last center frequency that was set in zero-span. Hope this helps.
Regards,
A.J.