That's an issue I've noticed too. Unfortunately not even a remote idea for a fix, as even removing the airport files does not help. It hasn't bothered me too much, but can see how it'd be really annoying for some.
I am 99% sure the problem is within the runway textures, included in the Optional Textures, and if that is the case it would need changes done by the developers.
@toby23 Just so everyone is aware, this is not an issue with the Black Square product, which works as intended. It happens when developers do not follow the official guidelines for taxi sign usage. I have since been in touch with the developer, who has fixed the problem for me. I have also spoken with the developer of the airport in question and they have explained why they did what they did too. Just so this is clear, this is not an issue with Black Square's product.