Originally reported for 4.4.0 and seemed fixed for 4.4.2. However reproducible again for gnuplot 4.6.0.
Originally reported at Debian bug tracking system (BTS) as
From original submitter (Terry Bullett),
I use gnuplot in bash scripts which create gnuplot command files and
then call gnuplot to make the files. Version 4.4.0 will enter a state
of 'T' (stopped) when the parent bash script is running in the background.
Executution is normal when the parent script is in the foreground.
An update to 4.4.2 has resolved this problem, but this version is not in
the Debian squeeze package.
However, this seems to have been reintroduced somewhere later (Ron)
$ gnuplot sweep-plot.script &
$ ps xau | grep gnuplot
ron 13484 0.0 0.2 318804 19300 pts/4 S 04:13 0:00 gnuplot
ron 14136 0.0 0.0 256540 6732 pts/4 S 04:16 0:00 gnuplot
ron 17479 0.0 0.0 77880 2112 pts/4 T 05:02 0:00 gnuplot sweep-plot.script
ron 17481 0.0 0.0 8028 844 pts/4 S+ 05:02 0:00 grep gnuplot
+ Stopped gnuplot sweep-plot.script
So this is either still not fixed in 4.6.0-1, or has been reintroduced again.
I can reproduce this even with a minimal gnuplot file
$ cat minimal.gp