Why won't my form post back after validation?

Question

I have an asp.net page with multiple validation summaries setup with ShowMessageBox="True" and several validators. I have run into a situation where when validation fails the validation summary displays correctly but then the next click that would normally trigger a postback of the page does not trigger a postback. So the steps look like this:

1. Click button that triggers validation.
2. Validation fails and a messagebox with the failure message is displayed.
3. Click a different button which does not validate but should trigger a postback nothing happens
4. Click same button as step 3 again postback happens as expected.

What could cause this behavior?

EDIT: The validation was being done in the following manner. In the asp page:

<asp:Button runat="server" id="btn" onClientClick="return DoValidation();" />

In the javascript:

function DoValidation() {
    if (!Page_ClientValidate('group1'))
        return false;
    if (!Page_ClientValidate('group2'))
        return false;

    return true;
}

Answer 1

After working on this and making careful use of the debugger I finally found out that when you do validation the way described in the edit to the question a boolean is set on failure that blocks the next PostBack of the page from going through. I believe this is done when validation is being done automatically instead of explicitly as I'm doing here. Changing the javascript described above to look like this:

function DoValidation() {
    if (!Page_ClientValidate('group1')) {
        Page_BlockSubmit = false;
        return false;
    }
    if (!Page_ClientValidate('group2')) {
        Page_BlockSubmit = false;
        return false;
    }

    return true;
}

Causes the problem to go away. Hopefully this will help the next person who makes the same mistake I did.