How to reproduce:

• You'll need two kits.
• Remove the compiler from kit A. Make sure that kit B is functional.
• Switch your project (qbs for example) to kit A.
• Wait until parsing etc. is done. The build button is now disabled.
• Switch your project's kit to B (the working kit).

What happens:

• The build button will not be enabled. Even reparsing the qbs project does not help.

What should happen:

• Changing to the functional kit B should reparse the project and enable the build button.