1) Create style with SLD containing one rule with some filter and one rule with <sld:ElseFilter /> tag.
2) Assign style to a vector layer (I used PostGIS based) with several features matching provided SLD rules
3) Open layer preview for the layer and click on objects to view their info
Info is displayed for all features of layer both for those correspoding to Filter-Rule and to ElseFilter-rule.
Info is not displayed when clicking on features handled by ElseFilter rule in SLD. For features handled by Filter-Rule it works fine.
It seems like WMS GetFeatureInfo request could not get features classified by ElseFilter-rule.