Flex 3.5 compile error

I encountered the following flex compile-time errors (using flex sdk 3.5.x):

1046: Type was not found or was not a compile-time constant: ModelLocator.

1120: Access of undefined property be.

while trying to compile an ActionScript3 file containing:

...
private var model1:be.myPackage1.ModelLocator = 
   be.myPackage1.ModelLocator.getInstance();		
private var model2:be.myPackage2.ModelLocator = 
   be.myPackage2.ModelLocator.getInstance();
...

I had to import these classes explicitly in order to make the error go away.

...
import be.myPackage1.ModelLocator
import be.myPackage2.ModelLocator
...

The weird thing is that I copied the variable assignments from a class that does compile, even without the explicit imports.