Simple Select-Dropdown for a NavigationProperty - odata

Question

For a current project, we're using Olingo in backend for OData v4 data access and openui5 as frontend framework. We know, that odata v4 is in a more experimental state in openui5 but we're doing not so bad with it. As it is normal for us, to use a workaround here and there, we're struggeling with following problem right now where I think there should be a really simple way instead of building a workaround.
Simplified oData v4 Model:
<EntityType Name="Notification">
<Key>
<PropertyRef Name="uid"/>
</Key>
<Property Name="uid" Type="Edm.Int32"/>
<Property Name="recievedAt" Type="Edm.Date"/>
<NavigationProperty Name="NotificationType" Type="rest.odata.BaseData" Nullable="false"/>
</EntityType>
<EntityType Name="BaseData">
<Key>
<PropertyRef Name="key"/>
</Key>
<Property Name="key" Type="Edm.String"/>
<Property Name="title" Type="Edm.String"/>
</EntityType>
The BaseData-Entity is used for different key-value-lists - in this case for a NotificationType. We have couple of types summarized and represented in an EntitySet:
<EntitySet Name="basedataNOTIFICATIONTYPES" EntityType="rest.odata.BaseData"/>
Now we're struggeling in the frontend with a simple sap.m.Select-Dropdown which should define the NotificationType of our Notification.
The Select-Control is defined like this:
var oControl = new sap.m.Select(sName, {selectedKey: "{NotificationType/key}"});
oControl.bindItems({
path: "/basedataNOTIFICATIONTYPES"
})
(I simplified the code very much)
The parent form is binded to a specific /Notification context.
This is what happens: The Select-Dropdown shows the current saved NotificationType of our specific /Notification. If I select another NotificationType from the dropdown, ui5 sends a PATCH Request to the EntitySet /basedataNOTIFICATIONTYPES. This is not the behaviour I expected. I need a PATCH Request sent to the specific /Notification(XXX)/NotificationType/key to update it.
Has anyone a hint for me?
Thanks in advance! :-)