WebUI only - deleted custom attribute id's can be re-used

I using RTC 4.0 GA,  and found that deleted custom attribute id's can be re-used in the WebUI.

steps I used: (WebUI)
- create a PA - SCRUM
- add an attribute - type = Large HTML, id = mylargehtml
- save
- delete this attribute
- save
- recreate a new attribute type = Large HTML, id = mylargehtml
- save
--> observed: PA is saved without error
--> expected: error should be raised as attribute id, though archived, can't be reused (example: Eclipse UI will throw an error and disable the Add attribute button in this case)

is this a defect?