At 6th level Bladebound Magus get their first Magus Arcana. When chosen it gives the option to choose which magus arcana you want, so that works fine
What isn't working is that if at level 6 (or lower) you select Bonus Magus Arcana as one of your Favored Class Bonus it does not allow you to choose what the Arcana is
I believe a fix would be to add +1 to Magus Arcana Remaining when Bonus Magus Arcana is chosen from level 6 for Bladebound Magus
In the attached screenshot you can see that Magus Arcana shows 1 (remaining 0), this is the 6th level choice which on the right hand side is Arcane Accuracy.
The 6th level Favored Class Bonus of Bonus Magus Arcana is doing nothing
As far as I can tell from the screenshot, you need to select "Bonus Magus Arcana" 6 times before you get a new one. Your picture shows that you have selected it only once (and 5 skill points).
is correct. The favored class bonus says "DESC:Magus: The magus gains 1/6 of a new magus arcana." implying you gain a new one when you take the fcb six, twelve and eighteen times.
nothing to fix.
Ok, thank you. New to Pathfinder and did not realise that it was a fraction