Resolution:
Using BC EDI 5.x, the HL action settings in action filter file need to be modified in order to
treat HL indexes with and without leading zeros equally.

To do that, the actions-x12.ecs file in $BC_HOME/protocols/edi/tpcl/config needs to be modified as follows :

-          back up the existing file
-          open file in SpecBuilder
-          go to SelectedNode with UniqueKey as "TransactionX12'
-          select action with name "EDIHierarchyChecker2" within its
ActionCollection
-          select Parameter with Name as "nStartValue"
-          update its value to "1n" where 1 is expected starting value
that can be replaced by a required number; "n" character after number
sets a requirement to ignore leading zeros in HL indexes.
-          save the file

Restart BC to pick up the file.