After adding a jar full of custom tags (written as JSP scriptlets) to my project, Tomcat insisted on compiling every page plus the tags from the jar on every page access. Needless to say, performance was a bit pedestrian.
Since then, I have researched the problem, but unfortunately it came right of its own accord - I cannot reproduce it. But I did notice that the re-packaged .war file emiited to Tomcat has all the file modification dates set to "now". I suspect the issue may arise when a run of the deploy tool spans two windows clock ticks.
The fix is trivial - I will attach an updated source file