diff --git a/block.tcc b/block.tcc
index 1979bd2..16c1f7a 100644
--- a/block.tcc
+++ b/block.tcc
@@ -112,9 +112,10 @@ block_manager<BlockSize>::write_lock_zero(block_address location)
 
 	buffer buf;
 	zero_buffer(buf);
+	register_lock(location, WRITE_LOCK);
 	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_),
 			      bind(&block_manager<BlockSize>::write_release, this, _1));
-	register_lock(location, WRITE_LOCK);
+
 	return write_ref(b);
 }
 
diff --git a/block_t.cc b/block_t.cc
index 2e68a24..c42c13e 100644
--- a/block_t.cc
+++ b/block_t.cc
@@ -92,7 +92,6 @@ BOOST_AUTO_TEST_CASE(different_block_sizes)
 		BOOST_CHECK_EQUAL(sizeof(rr.data()), 4096);
 	}
 
-
 	{
 		block_manager<64 * 1024> bm("./test.data", 64);
 		auto rr = bm.read_lock(0);
diff --git a/space_map_disk_t.cc b/space_map_disk_t.cc
index 015ec60..ea8729f 100644
--- a/space_map_disk_t.cc
+++ b/space_map_disk_t.cc
@@ -11,7 +11,7 @@ using namespace persistent_data;
 //----------------------------------------------------------------
 
 namespace {
-	block_address const NR_BLOCKS = 1023;
+	block_address const NR_BLOCKS = 10237;
 	block_address const SUPERBLOCK = 0;
 	unsigned const BLOCK_SIZE = 4096;
 
@@ -105,4 +105,18 @@ BOOST_AUTO_TEST_CASE(test_set_count)
 	BOOST_CHECK_EQUAL(sm->get_count(43), 5);
 }
 
+BOOST_AUTO_TEST_CASE(test_set_effects_nr_allocated)
+{
+	auto sm = create_sm_disk();
+	for (unsigned i = 0; i < NR_BLOCKS; i++) {
+		sm->set_count(i, 1);
+		BOOST_CHECK_EQUAL(sm->get_nr_free(), NR_BLOCKS - i - 1);
+	}
+
+	for (unsigned i = 0; i < NR_BLOCKS; i++) {
+		sm->set_count(i, 0);
+		BOOST_CHECK_EQUAL(sm->get_nr_free(), i + 1);
+	}
+}
+
 //----------------------------------------------------------------
diff --git a/transaction_manager_t.cc b/transaction_manager_t.cc
index 08b4ecb..657fa5d 100644
--- a/transaction_manager_t.cc
+++ b/transaction_manager_t.cc
@@ -18,6 +18,7 @@ namespace {
 		block_manager<4096>::ptr bm(new block_manager<4096>("./test.data", NR_BLOCKS));
 		space_map::ptr sm(new core_map(NR_BLOCKS));
 		transaction_manager<4096>::ptr tm(new transaction_manager<4096>(bm, sm));
+		tm->get_sm()->inc(0);
 		return tm;
 	}
 }
@@ -37,20 +38,29 @@ BOOST_AUTO_TEST_CASE(shadowing)
 
 	auto sm = tm->get_sm();
 	sm->inc(1);
-	auto p = tm->shadow(1);
-	auto b = p.first.get_location();
-	BOOST_CHECK(b != 1);
-	BOOST_CHECK(!p.second);
-	BOOST_CHECK(sm->get_count(1) == 0);
+	block_address b;
 
-	p = tm->shadow(b);
-	BOOST_CHECK(p.first.get_location() == b);
-	BOOST_CHECK(!p.second);
+	{
+		auto p = tm->shadow(1);
+		b = p.first.get_location();
+		BOOST_CHECK(b != 1);
+		BOOST_CHECK(!p.second);
+		BOOST_CHECK(sm->get_count(1) == 0);
+	}
+
+	{
+		auto p = tm->shadow(b);
+		BOOST_CHECK(p.first.get_location() == b);
+		BOOST_CHECK(!p.second);
+	}
 
 	sm->inc(b);
-	p = tm->shadow(b);
-	BOOST_CHECK(p.first.get_location() != b);
-	BOOST_CHECK(p.second);
+
+	{
+		auto p = tm->shadow(b);
+		BOOST_CHECK(p.first.get_location() != b);
+		BOOST_CHECK(p.second);
+	}
 }
 
 BOOST_AUTO_TEST_CASE(multiple_shadowing)