Agilent Technologies ESA Series User's/Programmer's Reference page 296

Remote Command Reference
INSTrument Subsystem
NOTE If you are using the status bits and the analyzer mode is changed, the status bits
should be read, and any errors resolved, prior to switching modes. Error conditions
that exist prior to switching modes cannot be detected using the condition registers
after the mode change. This is true unless they recur after the mode change,
although transitions of these conditions can be detected using the event registers.
Changing modes resets all SCPI status registers and mask registers to their
power-on defaults. Hence, any event or condition register masks must be
re-established after a mode change. Also note that the power up status bit is set by
any mode change, since that is the default state after power up.
Example:
Factory Preset:
Front Panel
Access:
296
INST:SEL 'CDMA'
Persistent state with factory default of Spectrum Analyzer mode
MODE
Chapter 5