OutOfMemory error when running the functional tests on Tomcat 5.5.20 on JDK 1.5

We've currently got a problem, where Tomcat seems to be running out of heap space, when running JIRAs functional tests.

About a week ago, this test started failing with OutOfMemory errors. I realize that increasing the maximum memory will probably get rid of this problem, but we've never had problems running the func tests with 256MB in the past, and we want to make sure we haven't introduced a memory leak. We examined the heapdump produced, and it looks like a large amount of the memory is retained by the org.apache.jasper.compiler.JspRuntimeContext (138 MB to be exact).

It seems that the 'jsps' SynchronizedMap is taking up all the space. The problem does NOT occur on Java 1.6.

Need to investigate if it is normal behavior for the JspRuntimeContext to take up this much memory?