tombstone WARN in log file when creating a table with many columns

I created a table with 500 columns, creating the table resulted in a warning in the log file.

WARN 10:13:17 Read 2504 live and 1003 tombstoned cells in system.schema_columns (see tombstone_warn_threshold). 2147483647 columns was requested, slices=[table_0-table_0:!], delInfo={deletedAt=-9223372036854775808, localDeletion=2147483647}

See the attached unit test.

I analyzed the table to understand what are the tombstone columns and it appears that Cassandra creates deleted columns for "index_type" and "index_name" if they are not present for a column.
"index_type" get the String value "null" if it is not present.
A side effect is that these deleted columns are not removed. Since system.schema_columns rarely changes compaction never happens for this table and the sstable will retain the deleted columns.