Comment 4 for bug 798095

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=586751 mentions commit 163d5fc3 which was supposed to fix the problem.

commit 163d5fc355670722ce45893e5af60ea4bde06a82
Author: Richard Hughes <email address hidden>
Date: Mon Sep 20 16:22:45 2010 +0100

    Do not continue to poll the serial port if there is no Watts Up Pro adaptor

diff --git a/src/linux/up-device-wup.c b/src/linux/up-device-wup.c
index 73bb8e5..bf5dbb8 100644
--- a/src/linux/up-device-wup.c
+++ b/src/linux/up-device-wup.c
@@ -376,11 +376,7 @@ up_device_wup_coldplug (UpDevice *device)

        /* coldplug */
        egg_debug ("coldplug");
- up_device_wup_refresh (device);
-
- /* hardcode true, as we'll retry later if busy */
- ret = TRUE;
-
+ ret = up_device_wup_refresh (device);
 out:
        return ret;
 }

However, up_device_wup_refresh() returns TRUE unconditionally, and has always done so since 163d5fc3. It looks like the "fix" has never been tested. This doesn't look like a regression.