Updating Assignment Notes using PSI interface

Hi,

We use PSI interface to update ASSIGNMENT NOTES field according specification on: http://msdn.microsoft.com/en-us/library/office/bb428845.aspx

Basically it works fine, however I have a question about NOTES field update.

We produce ChangeXML to update note and send via web service:

<Changes><Proj ID="c7a95eef-f0d3-4798-9ae9-9bffd9140206"><Assn ID="550c2759-66e7-43b8-bbe1-4cd89a8fa0f7" ResID="e527eed6-139f-4fee-bbb5-5d0926581a50"><Change PID="251658287">note 1</Change></Assn></Proj></Changes>

We have 2 cases here:

1.       User is the Project Manager. System update NOTES and we can see it in bottom notes field via PWA web interface (MY TASKS->TASK DETAILS section). It is also logged in “Recent Task Changes” section; however NOT INSERTED  in NOTES upper text area section.
2.       User is a Team Member. After update NOTES is logged in “Recent Task Changes” sections, however does NOT appear in neither one NOTES section. Also we noticed that updating NOTE via PWA web interface note is inserted into top NOTES field, what differs from PSI ChangeXML interface.

What is wrong here, and why there are different behaviors for different users?