NS_BINDING_ABORTED - why browser unexpectedly transform POST request to GET request

Currently I’m working with ancient ASP site (not ASP.NET), I write very simple JS script for submitting form for Delete button and checkbox list. In that script I simple add one parameters and want to submit form to each marked checkbox.

   function frmsubmit()
        if (document.frmdel.chklist[i].checked==true)
            var subsid = document.frmdel.chklist[i].value;
            document.forms['frmdel'].action = "edit_grp.asp?grpdel=T&grp=<%=Request.QueryString("grp")%>&subsid=" + subsid + "&ShowAll=<%=ShowAll%>";   
            return true;

Also I have connected to debugger on server

I expect a serials of postback depends how many records need to delete.
But I see something understandable for me - browser abort my Post request and server receive GET request. Moreover, I have changed Form action, but browser always ignoring my changing on “document.forms[‘frmdel’]” and using URL from Browser Location.

Most interesting that time on time (I’m looking to this marvel half of day) Browser finally send correct POST record, in this case records marked by checkbox deleted. As a result I start with 20 records in this group, but currently has only 3, 17 records deleted for 3-4 hours, but I click more than 100 times.

I checking cache policy, but in any place what I know I see just NoCache.

What can a reason of this strange issue?

You are changing the method of the form object, but you aren’t changing the HTML form. From the MDN description of method:

This value is overridden by formmethod attributes on <button> , <input type="submit"> , or <input type="image"> elements.

This forum isn’t very active. I suggest using Matrix. https://wiki.mozilla.org/Matrix

Ups, thank you, I understand reason of issue