SybaseIQ cursor over atemporary table behaves as read-only even if 'for update' was specified

Question

Hi, I'm attempting to update a temporary table using a cursor that was declared 'for update'. The update does not work: [Error Code: 7732, SQL State: 42W30] ASA Error -633: Update operation attempted on a read-only cursor

The sybase iq 12.7 docs says that the cursor becomes read-only under some circumstances, like for example if aggregated functions are used in the select. I paid attention to all these cases stated in the docs and I'm not doing anything illegal. Still, cursor is not updatable. Thank you for your help!