diff -up cups-1.3.5/backend/runloop.c~ cups-1.3.5/backend/runloop.c
--- cups-1.3.5/backend/runloop.c~	2007-08-22 19:34:34.000000000 +0100
+++ cups-1.3.5/backend/runloop.c	2008-01-09 15:37:44.000000000 +0000
@@ -216,7 +216,7 @@ backendRunLoop(
       FD_SET(CUPS_SC_FD, &input);
 
     FD_ZERO(&output);
-    if (print_bytes || !use_bc)
+    if (print_bytes || (!use_bc && !side_cb))
       FD_SET(device_fd, &output);
 
     if (use_bc || side_cb)