GW did fix the combi -weapon trait. In the current rule book it writes "...ammo for the two parts of the combi-weapon are tracked separately - if one profile runs out of ammo, the other can still fire, unless it has run out of ammo."
They have not changed the combi rules. The line you quoted has remained the same and shows the intent. My problem is with the line "When making an Ammo test for either of the weapons, roll twice and apply the worst result." The worst result for the weapon, which is described as a single weapon with two profiles
not two separate weapons (" A Combi-weapon has two profiles"), is that the whole weapon jams/runs out of ammo.
In the rules for ammo checks they do state it is not always running out of ammunition it can be weapon jams as well.
In the section you quoted it specifically says ammo, lower case, is tracked separately. If they used the word Ammo, case it would be clear that it applies to the status of Ammo in regards to Ammo Checks rather than the physical rounds. So the rule says you track the bullets separately not the Ammo check value.
It is still a poorly written rule subject to a lot of word and definition confusion. When they state it is a single weapon with two profiles they later refer to it as "either of the weapons" marking it a plural not a singular. Then later they say the ammo is tracked separately and links that to the word profile again making it a singular.
Is it a single weapon with two profiles or a pair of weapons with linked profiles? GW as written say it is both!
It would not take much ink to clear it up.
For my first quote all they need to do is replace "weapons" with profiles of, which adds a single letter and at the end of my first quote add "for that profile' which is 14 letters.
For a mere 15 letters that Combi rules would read far better.
It also does not help that they use Ammo as a status, in regards to Ammo Check, and ammo as a physical object, as in say Firestorm ammo.