Response for tracert different

Hello,

we'have got three Fortigates, one for each location (40C, 40C and 100D). Locations are connected via ipsec vpn tunnel. When I do a tracert to a device in the remote lan I am getting the following results: Location 1 100D (10.10.10.0) to 40C (10.10.20.0): 

tracert 10.10.20.100

Routenverfolgung zu PRINTER [10.10.20.100] über maximal 30 Hops:

1 1 ms 1 ms <1 ms fw-xy.com [10.10.10.123] 2 7 ms 6 ms 6 ms 10.10.20.123 3 6 ms 6 ms 6 ms PRINTER [10.10.20.100]

Location 2 (10.10.10.0) to 40C (10.10.30.0): 

tracert 10.10.30.100

Routenverfolgung zu PRINTER[10.10.30.100] über maximal 30 Hops:

1 <1 ms <1 ms <1 ms fw-xy.com [10.10.10.123] 2 10 ms 10 ms 10 ms 195.123.84.233 3 10 ms 10 ms 10 ms PRINTER [10.10.30.100]

I do not get why location 1 responds with the internal IP of the 40C and at location 2 the 40C responds with the external IP. Settings look fine/same.