Don't read if we chunked the input data.

st.c

@@ -1531,6 +1531,7 @@ ttywrite(const char *s, size_t n)
 				 * This means the buffer is getting full
 				 * again. Empty it.
 				 */
+				if (n < 256)
 					ttyread();
 				n -= r;
 				s += r;