diff --git a/src/mux_h1.c b/src/mux_h1.c
index 794740a79..ccdf3cdfa 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1020,10 +1020,15 @@ static void h1s_destroy(struct h1s *h1s)
 			h1c->state = H1_CS_IDLE;
 			h1c->flags |= H1C_F_WAIT_NEXT_REQ;
 			h1c->req_count++;
+
+			COUNT_IF(!(h1c->flags & H1C_F_IS_BACK) && b_data(&h1c->obuf), "front H1C switched in IDLE state with pending outgoing data");
+			COUNT_IF((h1c->flags & H1C_F_IS_BACK) && b_data(&h1c->obuf), "back H1C switched in IDLE state with pending outgoing data");
 			TRACE_STATE("set idle mode on h1c, waiting for the next request", H1_EV_H1C_ERR, h1c->conn, h1s);
 		}
 		else {
 			h1_close(h1c);
+			COUNT_IF(!(h1c->flags & H1C_F_IS_BACK) && b_data(&h1c->obuf), "front H1C swiched in CLOSED state with pending outgoing data");
+			COUNT_IF((h1c->flags & H1C_F_IS_BACK) && b_data(&h1c->obuf), "back H1C switch in CLOSED state with pending outgoing data");
 			TRACE_STATE("close h1c", H1_EV_H1S_END, h1c->conn, h1s);
 		}
 
@@ -1355,6 +1360,8 @@ static void h1_release(struct h1c *h1c)
 		sess_log(conn->owner); /* Log if the upgrade failed */
 	}
 
+	COUNT_IF(b_data(&h1c->ibuf), "H1C released with pending input data");
+	COUNT_IF(b_data(&h1c->obuf), "H1C released with pending output data");
 
 	b_dequeue(&h1c->buf_wait);
 	h1_release_buf(h1c, &h1c->ibuf);
@@ -3849,6 +3856,7 @@ static int h1_recv(struct h1c *h1c)
 	}
 	if (h1c->conn->flags & CO_FL_ERROR) {
 		TRACE_DEVEL("connection error", H1_EV_H1C_RECV, h1c->conn);
+		COUNT_IF(b_data(&h1c->obuf), "connection error (recv) with pending output data");
 		h1c->flags |= H1C_F_ERROR;
 	}
 
@@ -3887,6 +3895,7 @@ static int h1_send(struct h1c *h1c)
 
 	if (h1c->flags & (H1C_F_ERROR|H1C_F_ERR_PENDING)) {
 		TRACE_DEVEL("leaving on H1C error|err_pending", H1_EV_H1C_SEND, h1c->conn);
+		COUNT_IF(b_data(&h1c->obuf), "connection error (send) with pending output data");
 		b_reset(&h1c->obuf);
 		if (h1c->flags & H1C_F_EOS)
 			h1c->flags |= H1C_F_ERROR;
@@ -3916,6 +3925,7 @@ static int h1_send(struct h1c *h1c)
 	if (conn->flags & CO_FL_ERROR) {
 		/* connection error, nothing to send, clear the buffer to release it */
 		TRACE_DEVEL("connection error", H1_EV_H1C_SEND, h1c->conn);
+		COUNT_IF(b_data(&h1c->obuf), "connection error (send) with pending output data");
 		h1c->flags |= H1C_F_ERR_PENDING;
 		if (h1c->flags & H1C_F_EOS)
 			h1c->flags |= H1C_F_ERROR;
@@ -4318,6 +4328,9 @@ struct task *h1_timeout_task(struct task *t, void *context, unsigned int state)
 			return t;
 		}
 
+		COUNT_IF(b_data(&h1c->ibuf), "H1C timed out with pending input data");
+		COUNT_IF(b_data(&h1c->obuf), "H1C timed out with pending output data");
+
 		/* We're about to destroy the connection, so make sure nobody attempts
 		 * to steal it from us.
 		 */
@@ -4480,6 +4493,9 @@ static void h1_shutw_conn(struct connection *conn)
 	if (conn->flags & CO_FL_SOCK_WR_SH)
 		return;
 
+	COUNT_IF(b_data(&h1c->ibuf), "close connection with pending input data");
+	COUNT_IF(b_data(&h1c->obuf), "close connection with pending output data");
+
 	conn_xprt_shutw(conn);
 	conn_sock_shutw(conn, !(h1c->flags & H1C_F_SILENT_SHUT));
 
@@ -4893,6 +4909,7 @@ static size_t h1_done_ff(struct stconn *sc)
 			 */
 			h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 		}
+		COUNT_IF(b_data(&h1c->obuf) || sd->iobuf.pipe->data, "connection error (done_ff) with pending output data");
 		se_fl_set_error(h1s->sd);
 		if (sd->iobuf.pipe) {
 			put_pipe(sd->iobuf.pipe);
@@ -5072,6 +5089,7 @@ static int h1_fastfwd(struct stconn *sc, unsigned int count, unsigned int flags)
 		se_fl_set(h1s->sd, SE_FL_ERROR);
 		h1c->flags = (h1c->flags & ~H1C_F_WANT_FASTFWD) | H1C_F_ERROR;
 		COUNT_IF(h1m->state < H1_MSG_DONE, "H1C ERROR before the end of the message");
+		COUNT_IF(b_data(&h1c->obuf) || h1s->sd->iobuf.pipe->data, "connection error (fastfwd) with pending output data");
 		TRACE_DEVEL("connection error", H1_EV_STRM_ERR|H1_EV_H1C_ERR|H1_EV_H1S_ERR, h1c->conn, h1s);
 	}
 
@@ -5153,6 +5171,7 @@ static int h1_resume_fastfwd(struct stconn *sc, unsigned int flags)
 			h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 		}
 		se_fl_set_error(h1s->sd);
+		COUNT_IF(b_data(&h1c->obuf) || h1s->sd->iobuf.pipe->data, "connection error (resume_ff) with pending output data");
 		if (h1s->sd->iobuf.pipe) {
 			put_pipe(h1s->sd->iobuf.pipe);
 			h1s->sd->iobuf.pipe = NULL;