We've now been sent a Collectors Set from the same machine. Our set shows the Machins but sets were also printed on Birds 4 stock. As has been observed before the 10g Worldwide stamp is missing the weight, and thus has no indication of its value.
The 40g stamp has the weight in the correct font. The other 4 stamps have the weight in the original font.
It has been suggested that this happens when the machines are returned to a default setting. However in the original setting it was not possible to select 40g, and the Worldwide 10g stamp was not produced on the 'stamps for later' menu, but on the 'post now' menu (which otherwise used the wider non-pictorial label stock).
It remains to be seen how catalogue editors deal with the Faststamp variations. We know that some so-called errors have been produced, especially on Hytech machines, when the customer has pulled the free end of the strip, causing misprinting and sometimes blank labels in a strip of 7. Birds 2 & 3 have been legitimately used by post offices instead of Birds 4.
In the Stanley Gibbons Concise catalogue 2011 edition a separate catalogue number has been allocated to each of the 5 service indicators so clearly an additional number or sub-number will need to be used for the Machin, Birds 2 & 3 sets. (Birds 4 is not included in the 2011 edition and a 40g value was available on the first day, so its inclusion in the catalogue should not be a problem). There are also rumours that a part-roll of Birds 1 was used up in a machine after the upgrade and 40g stamps and/or collectors sets produced. Doubts have been cast upon the legitimacy of these if they exist. In the same way, until the truth about the circumstances of the production is known, one might question the use of Birds 2 at offices not originally supplied with that set.
Update: Birds 1 now confirmed legitimately issued from Cambridge - see here
But maybe Messrs Gibbons will revise the catalogue to a more logical 'by design' listing, with sub-numbers for the different values.
Finally here's an example of the 10g stamp with the missing value taken as a 40g stamp to make up the total for this 40g International Signed For item to Australia