e.g. see http://sdo-ganymede/Text
@RichardWallis will take a look. It's related to his recent improvements for that part of UI (multiple parent types) and to recent tweaks to the meta-model around datatypes.
Possibly related: #557 #218 #26
rdfs:Class > Text
http://www.w3.org/2000/01/rdf-schema#Class > DataType > Text
Suppress external class references in breadcrumbs (#660)
Improved fix to #660