This behavior is configured using <system.web><healthMonitoring>
element in web.config
. The default behavior is logging all unhandled exceptions and authentication failures to Application event log. There're two "rules" - one for the former and one for the latter.
So I just added this:
<healthMonitoring>
<rules>
<clear />
</rules>
</healthMonitoring>
which made those default rules disappear and the problem is solved for me. Note that this also removes the rule for logging unhandled exceptions which I don't need either.