Bug in Solr 6.6.0? Cannot change DocValues type from SORTED_SET to SORTED

[Stephan Schubert <St...@sick.de>]

After I tried an update from Solr 6.5.0 to Solr 6.6.0 (SolrCloud mode), I 
receive in one collection the following error:

"Cannot change DocValues type from SORTED_SET to SORTED for field 
"index_todelete". 

I had a look on the index values (if set all are true or not filled, 
checked via faceting in the working instance) and I can't see anything 
special issues on this field. In the case I move back to Solr 6.5.0 the 
Solr collection is coming up normal with the same set of index data. So I 
assume there was any change in 6.6.0 but couldn't find anything in the 
release notes nor in any known issues in JIRA.

Does anyone have an idea what's going on here? The field even doesn't have 
docValues set or multivalued, so I don't understand the error message 
here.

Configuration in schema.xml:
<field indexed="true" multiValued="false" name="index_todelete" 
stored="true" type="boolean"/>


Error Log:
java.util.concurrent.ExecutionException: 
org.apache.solr.common.SolrException: Unable to create core 
[GLOBAL-Fileshares-Index_shard1_replica2]
                 at 
java.util.concurrent.FutureTask.report(FutureTask.java:122)
                 at 
java.util.concurrent.FutureTask.get(FutureTask.java:192)
                 at 
org.apache.solr.core.CoreContainer.lambda$load$6(CoreContainer.java:586)
                 at 
com.codahale.metrics.InstrumentedExecutorService$InstrumentedRunnable.run(InstrumentedExecutorService.java:176)
                 at 
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
                 at 
java.util.concurrent.FutureTask.run(FutureTask.java:266)
                 at 
org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor.lambda$execute$0(ExecutorUtil.java:229)
                 at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
                 at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
                 at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.solr.common.SolrException: Unable to create core 
[GLOBAL-Fileshares-Index_shard1_replica2]
                 at 
org.apache.solr.core.CoreContainer.create(CoreContainer.java:935)
                 at 
org.apache.solr.core.CoreContainer.lambda$load$5(CoreContainer.java:558)
                 at 
com.codahale.metrics.InstrumentedExecutorService$InstrumentedCallable.call(InstrumentedExecutorService.java:197)
                 ... 5 more
Caused by: org.apache.solr.common.SolrException: Error opening new 
searcher
                 at 
org.apache.solr.core.SolrCore.<init>(SolrCore.java:977)
                 at 
org.apache.solr.core.SolrCore.<init>(SolrCore.java:830)
                 at 
org.apache.solr.core.CoreContainer.create(CoreContainer.java:920)
                 ... 7 more
Caused by: org.apache.solr.common.SolrException: Error opening new 
searcher
                 at 
org.apache.solr.core.SolrCore.openNewSearcher(SolrCore.java:2069)
                 at 
org.apache.solr.core.SolrCore.getSearcher(SolrCore.java:2189)
                 at 
org.apache.solr.core.SolrCore.initSearcher(SolrCore.java:1071)
                 at 
org.apache.solr.core.SolrCore.<init>(SolrCore.java:949)
                 ... 9 more
Caused by: java.lang.IllegalArgumentException: cannot change DocValues 
type from SORTED_SET to SORTED for field "index_todelete"
                 at 
org.apache.lucene.index.FieldInfo.setDocValuesType(FieldInfo.java:212)
                 at 
org.apache.lucene.index.FieldInfos$Builder.addOrUpdateInternal(FieldInfos.java:430)
                 at 
org.apache.lucene.index.FieldInfos$Builder.add(FieldInfos.java:438)
                 at 
org.apache.lucene.index.FieldInfos$Builder.add(FieldInfos.java:375)
                 at 
org.apache.lucene.index.MultiFields.getMergedFieldInfos(MultiFields.java:245)
                 at 
org.apache.solr.index.SlowCompositeReaderWrapper.getFieldInfos(SlowCompositeReaderWrapper.java:266)
                 at 
org.apache.solr.search.SolrIndexSearcher.<init>(SolrIndexSearcher.java:281)
                 at 
org.apache.solr.core.SolrCore.openNewSearcher(SolrCore.java:2037)
                 ... 12 more