Here are the steps to reproduce this bug:
1) Create a LABKEY.QueryWebPart():

<div id='WebPartBugDiv'/>
Ext4.onReady(function() {
    var qwp1 = new LABKEY.QueryWebPart({
        renderTo: 'WebPartBugDiv',
        schemaName: 'core',
        queryName: 'users'
    });
});

2) click on the header row of the email column and select 'Filter...' from the drop down menu.
3) Within the single dialog box, add two filters of the same filter type: contains 'foo' and contains 'bar'
4) click ok to close the filter dialog
5) note that filter status displayed under the button bar only lists "(Email CONTAINS bar)" and not "(Email CONTAINS foo) and (Email CONTAINS bar)"

This bug appears to be limited to the LABKEY.QueryWebPart(), as grids from java modules do not display this behavior. Also, repeatedly adding a single filter via the dialog box works, so it is something about adding two filters within a single dialog box. And adding two filters of different types within a single dialog box works.

-Will