Incorrect feedback following certain share operations

_Scenario_: This bug is easily seen for segments 4 and 5 on my development server (141.84.42.103:8003). Logged in as **bob2**, I GET /electrophysiology/segment/4/acl which indicates that segment_4 is shared with **ray**. By POSTing to .../acl, I change sharing to user **bob**. Both the immediate answer and subsequent GETs reflect this. However, the same operation for segment_5 results in curious behavior: The response to my POST indicates that sharing was successfully changed to **bob** (HTTP 200). A subsequent GET shows that no sharing change was made.

_Proposed solution_: I'm not certain what's at miss here. In any case, a failure to perform the requested change needs to be obvious and return an error code.