This is a builtin feature of the way the datatips work...by default there seems to be a rounding to 6 significant digits with the 'auto' format setting.
hL=plot([1 2],8388608*[1 1],'*-'); % the example large integer plotted
xlim(xlim+0.1*[-1 1]) % stretch x so points aren't identically on boundaries
hAx=gca;
hAx.YAxis.TickLabelFormat='%.1f'; % clean up y labels
hAx.YAxis.Exponent=0;
% the above is all just preliminaries; the issue about datatip display follows...
hL.DataTipTemplate
hL.DataTipTemplate.DataTipRows
hL.DataTipTemplate.DataTipRows.Format
[hL.DataTipTemplate.DataTipRows.Format]=deal("%d","%d");
will work for the present integer values; can be adjusted as needed for specific data sets.
hL.DataTipTemplate.DataTipRows.Format
Since the property is a member of the line it can't be set until the line is drawn unless one makes a change in the root property of the graphics root. That's doable either at the global level or for a specific figure or session depending upon needs.
