Update table with extending table column value

Hi,
I am trying to update single field value for the table via Linq but I face an exception:
NHibernate.Exceptions.GenericADOException: ‘could not insert/select ids for bulk update[SQL: insert into HT_EQUIPMENTTYPE SELECT equipmentt0_.ID as ID FROM EQUIPMENTTYPE equipmentt0_ inner join BACKBONEMEMBER equipmentt0_1_ on equipmentt0_.ID=equipmentt0_1_.ID inner join VERSIONABLE equipmentt0_2_ on equipmentt0_.ID=equipmentt0_2_.ID inner join PERSISTABLE equipmentt0_3_ on equipmentt0_.ID=equipmentt0_3_.ID WHERE NAME=? and MAJOR=? and MINOR=? and PATCH=?]’

I am not sure why this is trying to insert an entry into wrong table when it should do an single field value update instead.

The code to update field:

internal static void UpdateDescriptionForSpecificBackboneMember<TBackboneMember>(
			this ISession session, string name, string version, string newDescription)
			where TBackboneMember : BackboneMember
		{
			var versionInfo = new VersionInfo(version);
			var updateEntries = session.QueryOver<TBackboneMember>().Where(bbm => bbm.Name == name &&
				bbm.Major == versionInfo.Major && bbm.Minor == versionInfo.Minor && bbm.Patch == versionInfo.Patch)
				.Where(x => x.Description == newDescription);
			if (updateEntries.RowCount() > 0)
				return;

			var backboneMember = session.Query<TBackboneMember>().SpecificBackboneMember(name, version);
			backboneMember.UpdateBuilder().Set(x => x.Description, newDescription).Update();
		}

		public static IQueryable<T> SpecificBackboneMember<T>(
			this IQueryable<T> query, string name, VersionInfo version) where T : BackboneMember =>
			query.Where(bbm => bbm.Name == name &&
				bbm.Major == version.Major &&
				bbm.Minor == version.Minor &&
				bbm.Patch == version.Patch);

The hbm.xml truncated code is:

  <joined-subclass name="XXX.Configuration.BusinessObjects.EquipmentType, XXX.Implementation"
                   table="EQUIPMENTTYPE"
                   extends="XXX.Configuration.BusinessObjects.BackboneMember, XXX.Implementation">
    <key column="ID" />
    <property name="Name" column="NAME" length="200" unique-key="UQ_EQUIPMENTTYPE" index="IDX_EQUIPMENTTYPE_NAME" />
    <property name="Description" column="DESCRIPTION" />
    <property name="Configuration" type="BinaryBlob" column="CONFIGURATION" length="2147483647" lazy="true" />
  </joined-subclass>

  <joined-subclass name="XXXX.Configuration.BusinessObjects.BackboneMember, EafManagement.Implementation"
                   table="BACKBONEMEMBER"
                   extends="XXX.Core.Persistence.Versionable, XX.Core">
    <key column="ID" />

...
  </joined-subclass>

	<joined-subclass name="XXX.Core.Persistence.Versionable, XXX.Core"
						  table="VERSIONABLE"
						  extends="XXX.Core.Persistence.Persistable, XXX.Core" abstract="true">
		<key column="ID" />
		<property name="Major" column="MAJOR" not-null="true" />
		<property name="Minor" column="MINOR" not-null="true" />
		<property name="Patch" column="PATCH" not-null="true" />

	</joined-subclass>

As result Versionable table contains the version values and the value needs to be updated in the main EquipmentType table. The reason of this update approach to avoid the BLOB loading (Configuration column) which is sometime very big (10-100 MB) and this is causing performance problems.
Please advice how to fix the problem by avoiding standard update causing performance problems to update simple text field.

Thanks in advance.

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