Objects stored on PUT even when etags don't match on object-servers

We run a multi region cluster (version 2.7.1 although have also replicated in test with version 2.15.1)

One of our regions has a firewall/anti-malware appliance thingy and we have found that every so often uploading objects would fail. The error would be that the etags didn't match on all returning object servers and a 500 is returned to the user. (we tracked this down to it changing lines of http header data in the objects themselves but that is another story.....)

Even though the object PUT returned a 500 the object is stored and is listed in the container etc.

When querying all object servers for the object however we get a different etag for the dodgy region:

root@swift:~# curl -g -I -XHEAD "http://172.22.59.46:6000/sdh/256733/AUTH_0bdf024c921848c4b74d9e69af9edf08/etag-test/test-file"
HTTP/1.1 200 OK
Content-Length: 10
X-Backend-Timestamp: 1516754468.33842
Content-Type: application/octet-stream
Last-Modified: Wed, 24 Jan 2018 00:41:09 GMT
Etag: "b2cfa4183267af678ea06c7407d4d6d8"
X-Timestamp: 1516754468.33842
X-Backend-Data-Timestamp: 1516754468.33842
X-Backend-Durable-Timestamp: 1516754468.33842
X-Object-Meta-Mtime: 1516754458.990904
Date: Wed, 24 Jan 2018 22:47:37 GMT

root@swift:~# curl -g -I -XHEAD "http://172.22.59.43:6000/sdf/256733/AUTH_0bdf024c921848c4b74d9e69af9edf08/etag-test/test-file"
HTTP/1.1 200 OK
Content-Length: 10
X-Backend-Timestamp: 1516754468.33842
Content-Type: application/octet-stream
Last-Modified: Wed, 24 Jan 2018 00:41:09 GMT
Etag: "9d240a40422483b268a24371f9e357cf"
X-Timestamp: 1516754468.33842
X-Backend-Data-Timestamp: 1516754468.33842
X-Backend-Durable-Timestamp: 1516754468.33842
X-Object-Meta-Mtime: 1516754458.990904
Date: Wed, 24 Jan 2018 22:47:37 GMT

root@swift:~# curl -g -I -XHEAD "http://172.22.59.45:6000/sdc/256733/AUTH_0bdf024c921848c4b74d9e69af9edf08/etag-test/test-file"
HTTP/1.1 200 OK
Content-Length: 10
X-Backend-Timestamp: 1516754468.33842
Content-Type: application/octet-stream
Last-Modified: Wed, 24 Jan 2018 00:41:09 GMT
Etag: "b2cfa4183267af678ea06c7407d4d6d8"
X-Timestamp: 1516754468.33842
X-Backend-Data-Timestamp: 1516754468.33842
X-Backend-Durable-Timestamp: 1516754468.33842
X-Object-Meta-Mtime: 1516754458.990904
Date: Wed, 24 Jan 2018 22:47:38 GMT

Also upon inspecting the container dbs I see that one of the dbs contains the bad etag, the rest show the good etag so there are inconsistencies there too.

Should some swift process be fixing these inconstancies up somehow? or possibly not allowing the data to be stored at all?