IIS Rewrite rule seems happens twice

I have a simple rewrite rule as follows:

<rule name="short url" enabled="true" stopProcessing="true">
    <match url="(.*)" />
    <conditions logicalGrouping="MatchAll" trackAllCaptures="false">
        <add input="{REQUEST_URI}" pattern="redirect(.*)" negate="true" />
        <add input="{REQUEST_URI}" pattern="pages(.*)" negate="true" />
    </conditions>
    <action type="Redirect" url="/redirect?page={R:1}" appendQueryString="true" logRewrittenUrl="true" />
</rule>

However, if a put a breakpoint in our code on the redirect target page it gets hit twice.

Why would this happen?

Copyright Notice：Content Author:「Andrew Lindemulder」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/39167588/iis-rewrite-rule-seems-happens-twice