in build 070828

Repro steps:
- create a sequence diagram
- create and name a lifeline
- select the lifeline
- from the properties editor, click on Stereotypes entry to bring up the Stereotype editor
- click on Add button and type in a stereotype name, then press Enter, and click OK to close the Stereotype editor
- before doing anything else, from the properties editor, click on Stereotypes entry to bring up the Stereotype editor again
- click on the stereotype and type in some changes to the original stereotype and press Enter, click OK
Result: now the Stereotypes line on the properties editor shows 2 stereotypes separated by comma for the original and
modified stereotypes. If repeating the last steps to modify the stereotype again, another stereotype is duplicated.
There's still only one stereotype is listed in the Stereotype editor.
- click on an empty diagram area and select the same lifeline again
- from the properties editor, click on Stereotypes entry to bring up the Stereotype editor
Result: now Stereotype editor shows the multiple stereotypes one on each line