This issue occurs due to the presence of Cisco bug ID CSCse98282.
This happens when Firewall Services Module (FWSM) creates two xlates for one-flow-traffic from both inside/outside and outside/inside by mistake.
The only workaround for this issue is to downgrade the FWSM software version to 3.1(1). Refer to Cisco Catalyst 6000 FireWall Service Module 3DES Software in the Software Download page in order to download this version.
Troubleshoot software feature
Firewall - modules (FWSM)
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