Bug in RAID10 'enough' when far_copies=2?

Consider an array with raid_disks=4, near_copies=1, far_copies=2.

The function "enough" in raid10.c requires all four of these equations
to be true:
  Eqn0 := 0 || 1 // device 0 or 1 is present
  Eqn1 := 1 || 2
  Eqn2 := 2 || 3
  Eqn3 := 3 || 0

This behavior is specific to far_copies=2. When near_copies=2, only
Eqn0 and Eqn2 are required.

The documentation claims that for this configuration, the layout is:
  A1   A2   A3   A4
  A5   A6   A7   A8
  ..   ..   ..   ..
  A2   A1   A4   A3
  A6   A5   A8   A7

In this situation, the array should NOT be possible to reassemble from
(0, 1) or (2, 3). The 'enough' function rejects those; Eqn2 and Eqn0
fail respectively. The 'enough' function accepts (0, 2) and (1, 3),
which seems correct.

However, the 'enough' function REJECTS (1, 2) and (0, 3) due to Eqn3
and Eqn1 respectively. According to the documented layout, 'enough'
should accept these configurations.