sort -rn produces output different from gnusort

I have a file with the following content:

$ cat /tmp/sveta 
      1 lock/lock0lock.c line 5163
      1 lock/lock0lock.c line 3249
      1 fsp/fsp0fsp.c line 3395
      1 btr/btr0cur.c line 672
      1 btr/btr0cur.c line 450
      1 ./include/btr0btr.ic line 53

If I run gnusort on my file, I get the following results (expected):

$ gnusort -r /tmp/sveta 
      1 lock/lock0lock.c line 5163
      1 lock/lock0lock.c line 3249
      1 ./include/btr0btr.ic line 53
      1 fsp/fsp0fsp.c line 3395
      1 btr/btr0cur.c line 672
      1 btr/btr0cur.c line 450

With sort -nr I get a different order (pay attention for the last line):

$ sort -nr /tmp/sveta 
      1 lock/lock0lock.c line 5163
      1 lock/lock0lock.c line 3249
      1 fsp/fsp0fsp.c line 3395
      1 btr/btr0cur.c line 672
      1 btr/btr0cur.c line 450
      1 ./include/btr0btr.ic line 53

However, if I use pipe sort -n | sort -r, the results are the same as with gnusort:

$ sort -n /tmp/sveta | sort -r
      1 lock/lock0lock.c line 5163
      1 lock/lock0lock.c line 3249
      1 ./include/btr0btr.ic line 53
      1 fsp/fsp0fsp.c line 3395
      1 btr/btr0cur.c line 672
      1 btr/btr0cur.c line 450

Start by reproducing the issue with the provided /tmp/sveta input and compare sort -nr with sort -n | sort -r and GNU sort. Trace the sort command's handling of combined numeric and reverse flags, then verify that the output ordering matches GNU sort and add a regression test for this input.