SNMPv3: two request needed to get response(msgAuthorit ativeEngineTime)?

Hello, 
I am facing problem with SNMPv3 authentication on swithes. 

Linux with Net-SNMP 5.3.1.
When I run snmpget from the Linux console (eg. for Nagios) I get the correct response from the switch: 
snmpget -v3 -u snmpuser -l authpriv -a md5 -A abcd1234 -x des -X abcd1234 -e 800019560300E0B19BC33F 172.31.21.98 sysName.0
SNMPv2-MIB::sysName.0 = STRING: TestSwitch

But the switch sends a swnmp trap: Authentication failed

I've traced snmp with wireshark:
1. the first snmp request to the switch contained:
    msgAuthoritativeEngineID: 800019560300E0B19BC33F
    msgAuthoritativeEngineBoots: 0
    msgAuthoritativeEngineTime: 0
2. next cames from the switch snmp report with:
    msgAuthoritativeEngineID: 800019560300E0B19BC33F
    msgAuthoritativeEngineBoots: 1
    msgAuthoritativeEngineTime: 72848
3. second ??? snmp request to the switch contained:
    msgAuthoritativeEngineID: 800019560300E0B19BC33F 
    msgAuthoritativeEngineBoots: 1
    msgAuthoritativeEngineTime: 72848
4. snmp response from switch - OK

The only difference between 1. and 3 is msgAuthoritativeEngineBoots and msgAuthoritativeEngineTime .
How can I configure net-snmp for snmp v3 with auth. ? 

thanks

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