void updateFromXML(string url,boolean insert_new,boolean del_missed,function afterCall);
insert_new boolean insert new items (optional, true by default)
appears to be working backwards.
New updates dissapear with the option true; but remain in the grid with the option false.
Am I crazy? 
all parameters of the updateFromXML method work well for me locally.
for the insert_new for example, initially you’loaded the data, where you have the three row with the ids “1”,“2”,“3”.
then you are reloading the data with the enabled insert_new from the source where also you have the row with the id “4”. This row will be inserted to the grid. If the insert_new parameter is false - this row won’t be inserted to the grid.
If the problem still occurs for you please, provide with a complete demo or a demo link, where the mentioned problem can be reconstructed.