A user is unable to update the Units of Measure fields in Inventory Item records all together because SmartClient throws a warning when the Units Type field is populated.
In the NetSuite UI, the user has to set the value for the Units Type field in order for NetSuite to determine the units of measure that it will use for the remaining three fields (Stock, Purchase and Sale Units). A dialog box appears indicating "You have selected a units type for this item..." Once the Units Type field has been populated, it automatically populates the base unit value to the three fields with the plural value of the Units Type field value.
In SmartClient, the user must populate the Units Type column then update the record. The cell with the internal ID will be highlighted in yellow and the same dialog box in NetSuite (You have selected a units type for this item...) will appear when the cell is clicked. The next step is to right click the table and click Refresh Results Table. Once the table is refreshed, the three fields will be automatically populated with the base units just like the way it does it in the NetSuite UI. From hereon, the three fields can be changed with the appropriate unit of measure.
To sum things up, the dialog box in NetSuite prevents the SmartClient user from updating all four fields simultaneously. Whenever a warning appears in SmartClient, it throws a warning to the user and it stops updating the rest of the cells even though it's not an error. The same rule applies to any sublist in SmartClient.