From K1 entry control, Tax field shows empty even the GST Tax Code set is IM0. To reflect the desired value of Tax Field which is "N/A", re-select the Tax Code and pick the "IM0" again. Upon doing this, "Total Value of Standard Rated Acquisition" from GST-03 will also be correct.
***Usually encountered when using lower versions (701 and below) and once upgraded to higher (e.g. 704, 706) or latest (708) versions.