milestone in group problem

hi
this problem found on easysocial demo http://easysocial.stackideas.com

step by step :
1-
create a group
2-
go add atask
here you must to create the first milestone , please create it
3-
log in this milestone and creat new item
4-
delete this item
5-
delete the task (milestone) from the stream.
6-
now go to share a new task again
""you will find the old milestone listed on the form ""
add title and date then click to share .
7-
error message that say :
Sorry, but the content is currently not available or you do not have permissions to view the item.
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(maybe it is not problem and i dont understand what happen there !!!!)