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I think the right solution is to use clickAndWait command instead of click+pause because it always success contrary to click+pause (we dont known the page response time). I see no reason why you don't observe the same behavior with clickAndWait. Maybe it's because your are testing the login page that can be a little tricky to test due to the session handling.
To be sure to always start a test in a clean session, my tests always do the same actions :
1. logoff
2. login
3. check error
Here, an example of my standard login procedure under selenium from (http://labs.libre-entreprise.org/pluginsscm/scmcvs/cvswebviewvc.php/ofbizNeogia/neogia/manufacturing/webapp/manufacturing/tests/TestProcessRoutingTestCreateNomenclature.html?rev=1.2;content-type=text%2Fplain;cvsroot=neogiaroot=neogia&view=markup)

<!-- Begin of standard login procedure -->
<tr>
 <td>open</td>
 <td>/manufacturing/control/logout</td>
 <td></td>
</tr>
<tr>
 <td>type</td>
 <td>USERNAME</td>
 <td>admin</td>
</tr>
<tr>
 <td>type</td>
 <td>PASSWORD</td>
 <td>ofbiz</td>
</tr>
<tr>
 <td>select</td>
 <td>locale</td>
 <td>value=fr</td>
</tr>
<tr>
 <td>clickAndWait</td>
 <td>submitButton</td>
 <td></td>
</tr>
<tr>
 <td>assertElementNotPresent</td>
 <td>//div[@class='errorMessage']</td>
 <td></td>
</tr>
<!-- End of standard login procedure -->

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