Yeah, I don't know how long it's been but they have the same specs now. Wood Frames and wood blocks both have a mass of 5 and a horizontal support of 40. That gives you a horizontal block support of 8 blocks. The cobble and the concrete both state a mass of 10 and a horizontal support of 120. This gives you 12 blocks of horizontal support.
These numbers are as stated in the game. I've never found it to be different in practice either. That being said, I get that my build is likely pushing those limits. Did they just change it and forget to change the localization file or something?
Don't get me wrong, this issue only appears to happen when you upgrade blocks away from the supports. If you upgrade at the supports and then progressively move away from them, it doesn't seem to cause any collapse. It just doesn't make sense to me if the mass and horizontal support numbers aren't changed. It really shouldn't matter what blocks you upgrade as long as those numbers are the same. That is unless there is an unknown mechanic where it momentarily adds an extra bit of mass during the process of upgrading. I can't think of another reason why it would act like this.
Edit: spelling correction