why am i observant unsuitable javascript explanation function looping an alert() vs. but it?

i have formula identical filtering entries an array objects:

var filterregex = new regexp(".*blah.*","ig");
if (filterregex.test(events[i].thing) && events[i].show) {
    console.log("success: filtering thing " + i + " " + events[i].thing);
    events[i].show = false;
    numevents--;
}

i unsuitable law condition (checking firebug, both conditions loyal individually, nonetheless sometimes whole countenance evaluates false). however, i indeed put an alert() called inside matter (like line 4), becomes unchanging i outcome i want.

can anything wrong explanation tell me since it's always producing expected?