Header "Auto Fit All Columns" works not always the same

[Blama]

Hi Isomorphic,

please see this modified online sample (v10.1p_2017-10-05):

isc.ListGrid.create({
    ID: "countryList",
    height:224, width:"100%", alternateRecordStyles:true,
    autoFitWidthApproach:"both",
    canAutoFitFields:true,
    canSort:false,
    headerAutoFitEvent:"doubleClick",
    data: countryData,
    fields:[
        {name:"countryCode", title:"Flag Thumbnail", cellAlign:"center",
          type:"image", imageURLPrefix:"flags/16/", imageURLSuffix:".png"},
        {name:"countryName", title:"Country"},
        {name:"capital", title:"Capital"},
        {name:"continent", title:"Continent"}
    ]
})

This is the display after a headerMenu-AutoFit direct after start:

This is expected, as autoFitFieldsFillViewport defaults to true.

This is the display if you resize any (not necessary the autoFitField "country") prior to headerMenu-AutoFit:

This matches the design if you'd add autoFitFieldsFillViewport: false and headerMenu-AutoFit directly after the start.
So it seems resizing some column sets autoFitFieldsFillViewport: false.
I think this is not wanted behavior as I can't find anything on it in the docs.

Best regards
Blama