How can I solve a problem of labels disappear when I edit system form in UI?

Hi all,

I have a problem in Edit Form UI..

I created user defined fields of project form under project management module, and I added new tab with UI then I placed UDFs in that new tab and then save, from here it's fine

After saving my modifications I close SAP client and reopen it, if I click to my new tab in order to see my UDFs some labels disappear, I though it's a problem of new tab and I renamed Remarks tab then I added that UDFs but the problem is still same

How can I solve the problem of labels disappeared when I edit system form in UI?

Please anyone can help me