wmctrl -ci kills unspecified windows

[Bib]

Trying to workaround a bug in saucy poping up sleep warnings I think I found a misbehaviour in wmctrl:
here is the output:
 wmctrl -l |grep nergie
0x01801e7f 0 PC \Uffffffffergie (French locale Énergie copy/paste, correct display in terminal)
0x01801fd6 0 PC \Uffffffffergie
me@PC:~$ ./.myscripts
envir_utf8: 1
Invalid type of _NET_WM_NAME property.
Using window: 0x02c00002
envir_utf8: 1
X Error of failed request: BadWindow (invalid Window parameter)
  Major opcode of failed request: 20 (X_GetProperty)
  Resource id in failed request: 0x2c00002
  Serial number of failed request: 16
  Current serial number in output stream: 16

wmctrl closed an unselected window

here is the script:
#!/bin/bash
NumWarn=`wmctrl -l | grep 'nergie' | wc -l`
if [ "$NumWarn" -gt "0" ]; then
 WinIds=`wmctrl -l | grep 'nergie' | cut -f1 -d" " `
 for Id in $WinIds ; do
 wmctrl -v -ci $Id
 done
fi

[Bib (bybeu)]

Assumed 'man wmctrl' where OPTIONS must be specified before ACTIONS, I can consider I can't reproduce the bug when I issue wmctrl -i -c 0x.....