When I cancel a build during ANT all seems ok and the resource is released:

Releasing previously locked resource: 10101010101...
Resource 10101010101 successfully released.

But when I cancel a job while it's doing SVN updates, it will not release it's resource (no output as above in console + on the manage jenkins - nodes - master I see that resource still marked as "reserved") and then all next scheduled jobs starve. I only have a master node, no slave - so very simple setup.

It probably happens because the resource is "reserved" not "locked" so it doesn't have something to actually unlock, but it should also "unreserve". I tried it with default reservation time setting of 3 seconds and also with 0 seconds.