1.
If the entity is a router created by neutron, then there is no issue
since the commit takes care of this scenario.
E.g.

   ext          net1          net2
   |             |             |src1
   |---Router1---|---Router2---|src2
   |             |             |src3

2.
Your question is more about a SF performing routing/NAT.
E.g. In topoloy below, SF is a Router.
   

  ext           |--SF1        
   |            |             |--src1
   |---Router1--|--SF(Router)-|--src2
   |            |             |--src3
                |--SF2

In such a case, yes, you are right this commit will break things if only the logical-src-port is specified without the prefixes since it will insert the SRC IP address of SF(Router).

However, there are several easy workarounds for this.
1. - Specify the prefixes for the sources (most obvious one).
2. - Specify the SF(Router) interfaces to be router owned. (see below)

root@fs-10-145-105-24:/opt/stack/networking-sfc# neutron port-show 0f15bfa0-c522-4cc8-b04a-b2f92df2b7f1
+-----------------------+---------------------------------------------------------------------------
| Field                 | Value                                                                                                  |
+-----------------------+---------------------------------------------------------------------------
| admin_state_up        | True                                                                                                   |
| allowed_address_pairs |                                                                                                        |
| binding:vnic_type     | normal                                                                                                 |
| created_at            | 2017-02-21T20:49:48Z                                                                                   |
| description           |                                                                                                        |
| device_id             | 5f7d0f49-cbae-4f6d-9de5-773f37c9faf1                                                                   |
| device_owner          | compute:None                                                                                           |



If the above SF is doing routing or NAT, then change the device owner to be network:router_interface instead of nova:compute

neutron port-update --device-owner network:router_interface 0f15bfa0-c522-4cc8-b04a-b2f92df2b7f1
root@fs-10-145-105-24:/opt/stack/networking-sfc# neutron port-show 0f15bfa0-c522-4cc8-b04a-b2f92df2b7f1
+-----------------------+---------------------------------------------------------------------------
| Field                 | Value                                                                                                  |
+-----------------------+---------------------------------------------------------------------------
| admin_state_up        | True                                                                                                   |
| allowed_address_pairs |                                                                                                        |
| binding:vnic_type     | normal                                                                                                 |
| created_at            | 2017-02-21T20:49:48Z                                                                                   |
| description           |                                                                                                        |
| device_id             | 5f7d0f49-cbae-4f6d-9de5-773f37c9faf1                                                                   |
| device_owner          | network:router_interface       

If the device_owner is a router_interface, the commit will not mess with it (not insert its source IP into the flow classifier)