Thanks Tresesco, I've tried TEXT(SEQ_NO) but it was a different issue after all - I worked out what was eating it. It's soooo obscure .
The problem was I used a "group by" and forgot to put the [%My_Key] in the "group by". It never complained that anything was wrong though... so Qlikers, beware!! If you get an issue like this, check your "GROUP BY".
Here is the code:
, SEQ_NO & '|' & PROJECT_ID AS [%My_Key]
, SEQ_NO & '|' & PROJECT_ID <---- I forgot this
This was annoying -- hopefully, QlikView will put a warning in the next SR or show a syntax error. Because in SQL, this wouldn't run.