Taking a layer with an OBJECTID column defined as NOT NULL NUMBER(38), exporting it using sdeexport, and re-importing it causes the OBJECTID column to be incorrectly defined as NUMBER(10).
This is a known issue.
** This issue has been addressed in ArcSDE 9.0 Service Pack 3 (SP3)
Click on the link in Related Information below to download the Service Pack, if necessary. **