The tags in the String taglib which extend StringTagSupport are broken for 
containers which reuse tag handler instances. The problem is in 
StringTagSupport.java, where initAttributes() is being called from within 
doEndTag(). Since the container is not required to reinitialise the attributes 
for a tag handler instance if they have the same values - which they might do 
in a loop, for example - the tag produces incorrect results after the first 
call.

The fix is simply to remove the call to initAttributes() from doEndTag().