With only one content type selected, the invalid facet displays an error : 

Indexing field search criteria with path 'toto' refers to an unknown indexing field: toto
org.apache.avalon.framework.configuration.ConfigurationException: Indexing field search criteria with path 'toto' refers to an unknown indexing field: toto
    at org.ametys.cms.search.ui.model.impl.IndexingFieldSearchUICriterion.configure(IndexingFieldSearchUICriterion.java:197)
    at org.apache.avalon.framework.container.ContainerUtil.configure(ContainerUtil.java:202)
    at org.ametys.runtime.plugin.component.ThreadSafeComponentManager$ComponentFactory.configureAndStart(ThreadSafeComponentManager.java:359)
    at org.ametys.runtime.plugin.component.ThreadSafeComponentManager$ComponentFactory.newInstance(ThreadSafeComponentManager.java:378)
    at org.ametys.runtime.plugin.component.ThreadSafeComponentManager.initialize(ThreadSafeComponentManager.java:206)
    at org.ametys.cms.search.solr.CriteriaSearchUIModelWrapper.setFacetedCriteria(CriteriaSearchUIModelWrapper.java:130)
    at org.ametys.cms.search.solr.SolrQuerySearchAction.doSearch(SolrQuerySearchAction.java:124)
    at org.ametys.cms.search.cocoon.SearchAction.act(SearchAction.java:137)

I expect the same kind of error if the facet is not found at all on the multiple content types.

I guess that since this error can happen legitimately if only one content type has that facet, it has been ignored with multiple content types.

But I should get the error if all content types have this error.