iis rewrite outbound rule FilterByTags not working

I've got an outbound rule as shown below:

<outboundRules>
     <rule name="ChangeReferencesToOriginalUrl" patternSyntax="ExactMatch" preCondition="CheckContentType">
         <match filterByTags="None" pattern="http://oldDomain.com" />
         <action type="Rewrite" value="http://newDomain.com/blog" />
     </rule>
     <preConditions>
         <preCondition name="CheckContentType">
            <add input="{RESPONSE_CONTENT_TYPE}" pattern="^(text/html|text/plain|text/xml|application/rss\+xml)" />
         </preCondition>
     </preConditions>
</outboundRules>

When the filterByTags value is set to "None", the scheme works as expected - all instances of the old URL are replaced. Of course, this is clumsier than using just the "A" or "Link" tags. However, when I specify those tags as shown in the documentation (https://www.iis.net/learn/extensions/url-rewrite-module/url-rewrite-module-20-configuration-reference#Tag_Filters), the rewrite scheme is ignored and no URLs are replaced.

I'm on an Azure web app, and I think I'm logging FRT properly. It doesn't even record a file for this event. For the sake of testing, I can definitely make it log a file by screwing up the rules :)

What gives? How does one debug this kind of problem?