Build Tanya icon becomes enabled if Tanya goes in Helicopter (2nd Tanya cannot be built)

[ghost]

The icon for building a Tanya re-enables when Tanya has been built and has entered a Helicopter (a second Tanya cannot be built).

Steps to reproduce:
Build a Chinook Helicopter and a Tanya (and no repair bay)
Click on Barracks and note that Tanya icon is disabled the same way the mechanic icon is disabled.
Have Tanya enter a helicopter and click back on the barracks
Note the Tanya icon is now enabled