diff --git a/tests/issues/673/673.ino b/tests/issues/673/673.ino
new file mode 100644
index 00000000..9b0943fe
--- /dev/null
+++ b/tests/issues/673/673.ino
@@ -0,0 +1,52 @@
+/* -*- mode: c++ -*-
+ * Copyright (C) 2021  Keyboard.io, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <Kaleidoscope.h>
+#include <Kaleidoscope-OneShot.h>
+
+// *INDENT-OFF*
+KEYMAPS(
+    [0] = KEYMAP_STACKED
+    (
+        OSM(LeftShift), OSM(LeftControl), ___, ___, ___, ___, ___,
+        Key_A, Key_B, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___,
+        ___,
+
+        ___, ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___, ___, ___, ___,
+        ___, ___, ___, ___,
+        ___
+    ),
+)
+// *INDENT-ON*
+
+KALEIDOSCOPE_INIT_PLUGINS(OneShot);
+
+void setup() {
+  Kaleidoscope.setup();
+  OneShot.setTimeout(50);
+  OneShot.setHoldTimeout(20);
+  OneShot.setDoubleTapTimeout(20);
+}
+
+void loop() {
+  Kaleidoscope.loop();
+}
diff --git a/tests/issues/673/sketch.json b/tests/issues/673/sketch.json
new file mode 100644
index 00000000..43dc4c7e
--- /dev/null
+++ b/tests/issues/673/sketch.json
@@ -0,0 +1,6 @@
+{
+  "cpu": {
+    "fqbn": "keyboardio:virtual:model01",
+    "port": ""
+  }
+}
\ No newline at end of file
diff --git a/tests/issues/673/test.ktest b/tests/issues/673/test.ktest
new file mode 100644
index 00000000..ec6f9b85
--- /dev/null
+++ b/tests/issues/673/test.ktest
@@ -0,0 +1,59 @@
+VERSION 1
+
+KEYSWITCH OS_SFT   0  0
+KEYSWITCH OS_CTL   0  1
+KEYSWITCH A        1  0
+KEYSWITCH B        1  1
+
+# ==============================================================================
+NAME Issue 673
+
+RUN 4 ms
+PRESS OS_CTL
+RUN 1 cycle
+EXPECT keyboard-report Key_LeftControl # report: { e0 }
+
+RUN 4 ms
+RELEASE OS_CTL
+RUN 1 cycle
+
+RUN 4 ms
+PRESS OS_CTL
+RUN 1 cycle
+
+RUN 4 ms
+RELEASE OS_CTL
+RUN 1 cycle
+
+RUN 100 ms
+
+RUN 4 ms
+PRESS OS_SFT
+RUN 1 cycle
+EXPECT keyboard-report Key_LeftControl Key_LeftShift # report: { e0 e1 }
+
+RUN 4 ms
+RELEASE OS_SFT
+RUN 1 cycle
+
+RUN 4 ms
+PRESS OS_SFT
+RUN 1 cycle
+
+RUN 4 ms
+RELEASE OS_SFT
+RUN 1 cycle
+
+RUN 100 ms
+
+RUN 4 ms
+PRESS A
+RUN 1 cycle
+EXPECT keyboard-report Key_LeftControl Key_LeftShift Key_A # report: { 4 e0 e1 }
+
+RUN 4 ms
+RELEASE A
+RUN 1 cycle
+EXPECT keyboard-report Key_LeftControl Key_LeftShift # report: { e0 e1 }
+
+RUN 5 ms