Upgrade price puzzlement

I've just got had my filter forge free trial run out, and I was looking at the options to buy, I only got chance to try a few filters so I was still not sure if I wanted to get the proper one yet. Anyway, I didn't want to end up wasting money if I bought the starter edition and had to get a better one later, so I took a look at the upgrade page to see how much it would cost me if I went to a better edition later on.

Anyhow, I was rather puzzled by the pricing...

the pricing on the buy page are:

Starter-1 Edition $9
Starter-3 Edition $19
Starter-7 Edition $29
Basic Edition $99
Standard Edition $199
Professional Edition $299

but on the upgrade page, the pricing goes:

Desired upgrade:

From Starter-1 Edition (Windows)
to Starter-3 (Windows) $5
to Starter-7 (Windows) $10
to Basic (Windows) $45
to Standard (Windows) $95
to Professional (Windows) $145
From Starter-3 Edition (Windows)
to Starter-7 (Windows) $5
to Basic (Windows) $40
to Standard (Windows) $90
to Professional (Windows) $140
From Starter-7 Edition (Windows)
to Basic (Windows) $35
to Standard (Windows) $85
to Professional (Windows) $135
From Basic Edition (Windows)
to Standard (Windows) $50
to Professional (Windows) $100
From Standard Edition (Windows)
to Professional (Windows) $50

so if I buy Basic edition straight up, it would be $99
but if I got Starter 1 for $9, then upgrade from that for $45, total price $54

or I could get professional for $9 + $145 = $154 instead of $299

Can this possibly be right?

I'm very puzzled, is this really a loophole that Filter forge allow, or is there some kind of restriction on upgrading?

Quote
Mongoose King wrote: or I could get professional for $9 + $145 = $154 instead of $299

I can see in paying for professional directly I MAY have overpaid.. oops.

still the best program in the known universe (after they incorporate my suggestions)