[pilowsky]

I don't want seem needy or overly argumentative, but is ♣A4 really enough to be described as a 'new suit'?
Or is it 'new' in the sense that it isn't the original suit?
I thought 2♥ was the default rebid here.

Basic robots.

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[Stephen Tu]

It's standard playing 1nt forcing to rebid 2c on 4=5=2=2, not strong enough to reverse in spades, for humans. You could argue the robot's description isn't verbose enough, but that's often the case with GIB, and in any case the actual description is what you or bot partner is supposed to play for, on average, as 4522 exactly is going to be very rare compared to 3+ clubs.

It's better to rebid 2c than 2h, usually, because:
- if partner has 5+ clubs, clubs rates to be OK if partner chooses to pass or raise.
- you allow partner to get to 2d with 6+ diamonds
- partner should almost always pref to 2H with 2H anyway, without 5+ clubs. About the only time partner passes will be with 1/0 hearts, and with 5+ clubs. (passing with south hand is severe error. Can easily have enough for game, holding 10 pts, partner can have up to 18 unbal; it is normal to take pref to hearts or bid an aggressive 2nt to give yourself chance for game, and/or play higher scoring partial. Passing with this shape would only be justified with bare minimum and worse hearts/better clubs)
- rebidding 2H partner will assume 6. Partner may raise to 3h or 4h on that assumption and be disappointed on you not having that extra trump trick. Also he will pass and you will play 5-0 or 5-1 fit when maybe 6-2 diamond fit or 5-2/6-2 club fit was available.

[pescetom]

Looking at it another way, a 2H rebid really needs to show six cards here, so if 1NT is truly forcing then faking a minor is the only way out.

In a system where 1NT is semi-forcing many will pass with a minimum 4=5=2=2 (still going down on this layout, but 2H is even worse).

[thepossum]

With problem bidding systems sometimes you need to engineer strange rebids. Open 1S then bid 2H

Its borderline between 2H and oh dear what else can I bid. Maybe a pass

I remember when learning Acol that I was taught to always have your rebid prepared. Why aren't other systems like that