vb.net - Control freeze in chart while painting? -

i have windows form application with, among other things, dozen text boxes , chart control. modifying of textbox fires subroutine updates data in chart control.

in chart control there 5 series. adding tracking statements in various events of chart , subroutines have discovered the subroutines update chart data finish application freezes between prepaint event , postpaint event 3rd series of chart.

if left long enough finishes , application starts working again. also, happens combination of data , on 1 particular computer (a test computer, not development computer).

i'm looking suggestions or hints why happens.