Can not assign construction unit to one location

[MechFO]

I've owned Zhizdra for several turns, it has Railyard 1 not connected to the railnet.

I can priority repair but it has no option for me to manually assign a construction unit.

[Joel Billings]

Thanks for the save, I can duplicate that, and I can't explain it. I found one other nearby town without the ability to attach, but all others I checked allowed an attachment. I'll add this to our bug list. There may be a valid reason for this but I don't know what it is.