Unusual results from TO_SECONDDATE() function

I'm using the TO_SECONDDATE() function in HANA SQLscript to combine a date field in format YYYYMMDD with a time field in HH24MISS.  These are separate fields in a table.  So, my SQL is TO_SECONDDATE( BEWIDT || BEWIZT ).  This works fine *unless* the date is exactly '99991231' and the time is exactly '240000' (both are allowable maximum values).  All the other dates/times convert properly if I add a where BEWIDT <> '99991231' clause to the query!  No format is given.

The error that's being returned is:

"Could not execute 'select to_seconddate(BWIDT || BWIZT) dtm from SAPYP0.NBEW' in 131 ms 565 µs .

[303]: invalid DATE, TIME or TIMESTAMP value: search table error:  [6931] attribute value is not a date or wrong syntax;seconddate [here]seconddate(string sqladd(string "BWIDT", string "BWIZT")),(BWIDT = '99991231'[string], BWIZT = '240000'[string]); checkNull false"

Seems like a boundary condition?

Thanks in Advance for enlightenment,

  Donn