In many technical objects the first line of long text are copied to and from short text of object. You did not use a BAPI to create the object but the SAVE_TEXT FM so I suppose short text and first
characters of long text are no more related, also the flag "long text exists" may be initial, so behavior of display program unpredictable....
Check PLKO-TXTSP and PLKO-KTEXT.
Hint: there are KBA in OSS as 1982719 - Texts cannot be displayed - Usage of function module SAVE_TEXT.
Regards,
Raymond