I am working in QGIS 2.18.0 version.
My analysis involves using vector filed calculator for some operation. This new filed I am creating with an output filed type as Decimal number(integer). I wrote expression and it works fine but when I save it the field type changes to Whole number.
In above image SlopeRati was Decimal type and I created one more filed SlopeRati1 and stored orginal decimal values as STRING. After saving this later doest not change but earlier filed becomes Whole number.