Not sure why web container is looking in the config directory, it's probably something specific to the tag libraries that it looks if it could not find the library anywhere else.
Reading through your message, if your library is at
/glassfishv3/glassfish/domains/mdsTest1/applications/Appl/lib/jtb/bserv.jar
Shouldn't the MANIFEST Class-Path in your web module for the libary be
"lib/jtb/bserv.jar"?
One additional note, if you library is located at the root of the lib directory, such as lib/bserv.jar, you don't need to specify any manifest class path, it will automatically be available to all the component modules.
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