You are seeing a lot of this entry in Tomcat logs.
This is a minor bug that was introduced in Apache 6.0.35 and fixed in Apache 6.0.36. It is caused by parameters with more than one '&' character.
Confluence bundled Apache Tomcat is v6.0.35 so it is affected by the bug however no need to worry as it is not doing anything harm to the instance and it was more of an info/benign noise in the logs.
This is caused by a bug of Tomcat 6.0.35. It's fixed in Tomcat 6.0.36. Please see the changelog of Tomcat 6.0.36 in this http://tomcat.apache.org/tomcat-6.0-doc/changelog.html
Here are some test cases I did:
- CONF 5.4.2 - built-in Tomcat 6.0.35 has this issue. And then upgrading to Tomcat 6.0.36 -> fix this issue.
- CONF 5.3 - built-in Tomcat 6.0.35 has this issue. And then upgrading to Tomcat 6.0.36 -> fix this issue.