There appears to be a redundancy in the description of the "disown" builtin in bash(1). Version is 4.2.
disown [-ar] [-h] [jobspec ...] [...] If jobspec is not present, and neither -a nor -r is supplied, the shell's notion of the current job is used. [...] If no jobspec is present, and neither the -a nor the -r option is sup‐ plied, the current job is used. Here's a patch to remove one of the instances. $ diff -u bash.1_ORIG bash.1 --- bash.1_ORIG 2013-08-21 19:12:47.857956352 +0200 +++ bash.1 2013-08-21 19:13:58.541953745 +0200 @@ -7307,13 +7307,6 @@ .BR SIGHUP . If no .I jobspec -is present, and neither the -.B \-a -nor the -.B \-r -option is supplied, the \fIcurrent job\fP is used. -If no -.I jobspec is supplied, the .B \-a option means to remove or mark all jobs; the -- Thomas Hood