error MSB4067: The eleme nt <DeploymentModel> beneath element <Project> is unrecognized.

When using MSBuild 15.0, cleaning or building a solution which contains dtproj projects gives the following error:

Packages.dtproj(3,3): error MSB4067: The element beneath element is unrecognized.

When using MSBuild 14.0, the behaviour is better: it logs warnings (MSB4078) about unsupported projects:

warning MSB4078: The project file "Packages.dtproj" is not supported by MSBuild and cannot be built.

The latter behaviour is more desirable (for me, at least): I would like to able to build a solution in a configuration which includes the .dtproj files. This would allow me to include these projects when building the solution in Visual Studio, and to be able to use the same configuration when building the solution via an MSBuild script.

Is this change of behaviour a bug? The message certainly seems like it is attempting to parse the dtproj file into some structure to which it doesn't belong. If it is not, is there a way to downgrade the error MSB4067 to a warning, or to skip certain projects when building a solution? The /ignoreprojectextensions:.dtproj option does not prevent the error.