Requests are not in the same batch - odata

Question

I'm having several calls that should be launched in parallel in a single batch request. This requests are function import call and two read requests. sapui5 version is 1.38.17 and odata model v2 used in this issue.
Here is request calls.
var oContext = this.getView().getBindingContext();
var oModel = this.getModel();
oModel.setDeferredGroups(["CSC"]);
oModel.setChangeGroups({
"FunctionImport1": {
groupId: "CSC",
changeSetId: "CSC1",
single: false
},
"ToRead1Set": {
groupId: "CSC",
changeSetId: "CSC1",
single: false
},
"ToRead2Set": {
groupId: "CSC",
changeSetId: "CSC1",
single: false
}
});
oModel.callFunction("/FunctionImport1", {
method: "POST",
groupId: "CSC",
changeSetId: "CSC1",
urlParameters: {
"Arg1": oContext.getObject("GUID"),
"Arg2": "",
"Arg3": ""
}
});
var sGUID1= oContext.getObject("ToRead1/GUID");
var sGUID2 = oContext.getObject("ToRead2/GUID");
oModel.read(oModel.createKey("/ToRead1Set", { GUID: sGUID2 }), {
groupId: "CSC",
changeSetId: "CSC1"
});
oModel.read(oModel.createKey("/ToRead2Set", { GUID: sGUID2 }), {
groupId: "CSC",
changeSetId: "CSC1"
});
oModel.submitChanges({
groupId: "CSC"
});
Initially there was only callFunction and read operations calls.
After I noticed that requests are not in the same batch I added setDeferredGroup call, but that didn't helped. After that I tried to add setChangesGroups that didn't worked either.
Here is what sapui5 odata model is sending.
--batch_e90b-96a1-4abd
Content-Type: multipart/mixed; boundary=changeset_f22c-3b40-d8af
--changeset_f22c-3b40-d8af
Content-Type: application/http
Content-Transfer-Encoding: binary
POST FunctionImport1?Arg1='123123123123'&Arg2=''&Arg3='' HTTP/1.1
sap-contextid-accept: header
Accept: application/json
Accept-Language: en
DataServiceVersion: 2.0
MaxDataServiceVersion: 2.0
x-csrf-token: prD6hap9bHc_pk8kt1Q7pg==
Content-Type: application/json
--changeset_f22c-3b40-d8af--
--batch_e90b-96a1-4abd
Content-Type: application/http
Content-Transfer-Encoding: binary
GET ToRead1Set('') HTTP/1.1
sap-contextid-accept: header
Accept: application/json
Accept-Language: en
DataServiceVersion: 2.0
MaxDataServiceVersion: 2.0
x-csrf-token: prD6hap9bHc_pk8kt1Q7pg==
--batch_e90b-96a1-4abd
Content-Type: application/http
Content-Transfer-Encoding: binary
GET ToRead2Set('') HTTP/1.1
sap-contextid-accept: header
Accept: application/json
Accept-Language: en
DataServiceVersion: 2.0
MaxDataServiceVersion: 2.0
x-csrf-token: prD6hap9bHc_pk8kt1Q7pg==
--batch_e90b-96a1-4abd--
Notice that batch ids and changesSet ids are the same, so, logically it is the same batch for every request, but, in practice backend and SAP Netweaver Gateway Service thinks that it is a three separate batch requests.
So, the questions are
1. Is it SAPUI5 bug or Gateway bug, if it is a bug at all?
2. How can I put this requests into single batch requests without this psychical division of requests with --batch lines.
I'm beginning to think about catching the formed payload and manually cut --batch separators between requests for this particular case, because can't find another way to do that.