[Autumn]

The bonus damage for ghostwind when used in the same round as haunting does not apply if you have used another move before hand, for example.

Haunting > Attack(crit) > Ghostwind will not proc Ghostwind's 1.25x bonus damage.

[Neus]

How did you verify this?

[Snake]

That might be a critical hit with Fleur, which grants enough momentum to perform this:

Nothing -- (7M left)
Haunting (3M) -- (4M left)
Basic Hit [Critical!] (3M) -- (1M left, +2M due to Fleur)
Ghostwind (3M) -- (0M left)

This is 'how' you do it, whatever odd effects happening I don't know anything about it 'cuz I didn't test yet, but there you go. Also, this might be the only way to ever do this supposed 'bug'. Exploiting weaknesses for Momentum only grant +2M after two different skills hit weaknesses.

Might also be the wording. Ghostwind receives the bonus multiplier if you Haunting + Ghostwind normally, so the game's code would be expecting some sort of thing like:
--The last action done must be Haunting, so I can increase the damage in Ghostwind.
--If their last action is 'Basic Attack', then it does not make any sense to increase the damage in Ghostwind.
... Or something like that.

[Autumn]

Its as Snake says.

You use Haunting and then basic attack someone with any skill, if this skill crits and you are using Fleur you should have 3m left to use Ghostwind

[Neus]

That wasn't what I asked.

[Autumn]

I tested it in game and my damage was never boosted, I'll try again if you're getting different results, this time with debug.

This was done in singles matches in the arena.