a0d929ca_WSRP_v2_0_Specification__Statement_text
[#] CS079 [Section] 5.4.3 [Statement text] 
If the Consumer has set the portletState flag to "readOnly", the Portlet MUST NOT modify its persistent state regardless of whether it is persisted on the Producer or Consumer and MUST throw a fault message if processing the interaction requires changing its persistent state.
WSRP v2.0 Specification
Statement text