I guess I found it: the documentation for sap.ui.model.analytics.odata4analytics.Model uses an unsupported syntax for an optional method parameter:
* @param {object} mParameter?
Unfortunately, JSDoc doesn't complain and just pretends that the parameter is named "mParameter?". We propagate that into the sap.ui.core.js and Eclipse stops analysing it there:
sap.ui.model.analytics.odata4analytics.Model = function(oModelReference,mParameter?) {};
We'll fix that documentation in 1.28 and later. For 1.26, no more patches will be produced as 1.28 is already out now.