This bug in the JNLP APIs SingleInstanceService, which
I regard as being relatively 'obscure'* received 62 votes in
a single month (+ 2 days), and was fixed in the same time.
<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6631056>

Admittedly, the problem may have been intuitively obvious
from the source, but it is still heartenning that is was fixed
so quickly.  Good work, Sun.

* A quick survey of jobs in development suggest that most
require J2EE.  Since most J2EE apps. churn out HTML(+JS/AJAX)
rather than interact with Swing clients, it suggests rich client
GUI programming has become a relatively small section of
Java dev. in general.  Then, of that small amount of rich client
development, only some of those projects are launched using
web start.  And of those rich client's using web start, there
are only occasional apps. that have a need to run as a single
instance (or decide what to do with later invocations).