why does columns.insert transform displayindex datagridview (c#)?

i am inserting buttress datagridview programmatically (i.e., organization any information tables/databases) follows:

int lastindex = m_dgv.columns.count - 1;  // count = 4 case
datagridviewtextboxcolumn col = (datagridviewtextboxcolumn)m_dgv.columns[lastindex];
m_dgv.columns.removeat(lastindex);
m_dgv.columns.insert(insertindex, col);  // insertindex = 2

i have found columns visually out method infrequently controlling method. workaround manually set displayindex ability buttress afterwards. adding formula "fixes it", nonetheless i don't know since behaves way.

console.write(m_dgv.columns[0].displayindex); // value 0
console.write(m_dgv.columns[1].displayindex); // value 1
console.write(m_dgv.columns[2].displayindex); // value 3
console.write(m_dgv.columns[3].displayindex); // value 2
col.displayindex = insertindex;
console.write(m_dgv.columns[0].displayindex); // value 0
console.write(m_dgv.columns[1].displayindex); // value 1
console.write(m_dgv.columns[2].displayindex); // value 2
console.write(m_dgv.columns[3].displayindex); // value 3

as an aside, grid grow the buttress count dynamically. i wanted grow chunks, any insert didn't need buttress allocation (and compared initialization). any "new" buttress following total grabbing an new buttress end, inserting preferred position, origination visible.