Maybe I couldn't explain the issue, so I created this screencast:
http://www.screenr.com/NZZH
First, I'm running in IE9 mode, which displays the same behaviour as Chrome and Firefox. I click the button and it displays confirmation dialog. If I click OK, it continues and updates the page and changes the current time as expected. If I click cancel, it doesn't do anything, again as expected.
Then I'm switching to IE8. OK in confirmation dialog works as expected but if I click cancel there (0:42) it still refreshes the page and current time is changing.
Using Domino 9, with std. extlib coming with domino. Code is below:
<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core" xmlns:xe="http://www.ibm.com/xsp/coreex" style="margin:50px">
<xe:djButton label="Dojo Button" id="djButton1">
<xp:eventHandler event="onclick" submit="true"
refreshMode="partial" refreshId="computedField1">
<xp:this.action>
<xp:actionGroup>
<xp:confirm message="Really?"></xp:confirm>
<xp:setValue binding="#{viewScope.v01}" value="you did it!">
</xp:setValue>
</xp:actionGroup>
</xp:this.action>
</xp:eventHandler>
</xe:djButton>
<xp:br></xp:br>
<xp:br></xp:br><xp:br></xp:br>
Last Refreshed:
<xp:text escape="true" id="computedField1"
value="#{javascript:@Now()}">
<xp:this.converter>
<xp:convertDateTime type="time" timeStyle="medium"></xp:convertDateTime>
</xp:this.converter>
</xp:text>
</xp:view>