The BBoxStrategy in Lucene spatial requires a Lucene FieldType to use for its 4 numeric fields (e.g. configure doc-values, precisionStep, stored, indexed). Solr's FieldType doesn't directly expose a Lucene FieldType, unfortunately, so instead the Solr BBoxField as a hack creates a dummy value of one of the sub-fields corresponding to the suffix. But the sub-field names will also match the dynamic field pattern, assuming the dynamicField ends with a '*'. Furthermore, the sub-fields don't actually get registered with the schema properly in the dynamic field case.
The end result is that while attempting to get a dummy field value to get the Lucene FieldType, it inadvertently returns the spatial strategy field itself (not the numeric one) and calls createField which results in an IllegalStateException with an error that is pretty confounding.