In POM files of compat, impl, jstlel, spec modules of taglibs-standard-1.2.1 there is the following construct:

<build>
  <plugins>
    ...
    <plugin>
       <groupId>org.apache.maven.plugins</groupId>
       <artifactId>maven-checkstyle-plugin</artifactId>
       <version>2.6</version>
       <dependencies>
         <dependency>
           <groupId>org.apache.taglibs</groupId>
           <artifactId>taglibs-build-tools</artifactId>
           <version>1.2-SNAPSHOT</version>
         </dependency>
       </dependencies>
     </plugin>
    </plugins>
</build>

It is bad to depend on a SNAPSHOT version here, if anyone is rebuilding from this pom.  The current version is 1.2.3-SNAPSHOT, not 1.2-SNAPSHOT.

Apparently the version is not updated by maven-release plugin. Manually updating it is a bad idea.