diff --git a/libraries/chain/db_block.cpp b/libraries/chain/db_block.cpp
index c792344d..70fc79bb 100644
--- a/libraries/chain/db_block.cpp
+++ b/libraries/chain/db_block.cpp
@@ -353,8 +353,15 @@ signed_block database::_generate_block(
    {
       wlog( "Postponed ${n} transactions due to block size limit", ("n", postponed_tx_count) );
    }
+
    _pending_tx_session.reset();
 
+   // We have temporarily broken the invariant that
+   // _pending_tx_session is the result of applying _pending_tx, as
+   // _pending_tx now consists of the set of postponed transactions.
+   // However, the push_block() call below will re-create the
+   // _pending_tx_session.
+
    pending_block.previous = head_block_id();
    pending_block.timestamp = when;
    pending_block.transaction_merkle_root = pending_block.calculate_merkle_root();
@@ -363,6 +370,7 @@ signed_block database::_generate_block(
    if( !(skip & skip_witness_signature) )
       pending_block.sign( block_signing_private_key );
 
+   // TODO:  Move this to _push_block() so session is restored.
    FC_ASSERT( fc::raw::pack_size(pending_block) <= get_global_properties().parameters.maximum_block_size );
 
    push_block( pending_block, skip );