PO fields Order

Hi

I found a weird error today when i was creating PO.

The fields were not appearing in the correct sequence.

Normally in the item level, we have fields:-

Item Acc. Asst Item Cat. Material quantity UoM Delivery data ........etc

But today the fields were appearing like:-

Item material quantity Plant Sloc Returns Indicator Acc.Asst UoM Item Cat,,,,,,,etc

Why this happened and how to correct this,

Regards

Amit