Hi Sau,
I do not quite understand your question. Do you mean that you are typing in a label (within your stretched renderer)? If so, which version of ArcGIS are you using? There was a bug in which the label was not properly being saved. I beleive this was fixed in ArcGIS 9.3.1sp1.
If you were trying something else, please help me understand your issue a bit more.
If you are using ArcGIS 9.3.1sp1, and are still having this issue, please contact technical support.
Thanks,
Simon W.