pfSense

In System / Advanced / Miscellaneous / Load Balancing, I I filled out the field 'Sticky connections timeout' with 60. Then I clicked Save and the message 'The changes have been applied successfully.' was showed. But if I go another time to System / Advanced / Miscellaneous, the 'Sticky connections timeout' field is 0.
To bypass this problem I made a backup and modified two lines in XML file:

<lb_use_sticky/>
<srctrack/>

to:

<lb_use_sticky>yes</lb_use_sticky>
<srctrack>60</srctrack>

Then I restored the backup and rebooted the firewall. Finally worked.