Package install: LazarusPackageIntf not found

[winni]

Hello!

Strange error - not for the first time:

I am trying to install a package from a lpk file, in this case multithreadprocslaz.lpk .

Package is loaded; compile:

"LazarusPackageIntf not found"

Remedy:

In the package dialog look at the depencies: 

Required packages: FCL (..)
Click on FCL. It contains LazarusPackageIntf. Click on it.

Compile again. No errors anymore!!

First I want to tell this solution if other users have this problem,
because it took me some time to find this trick.

And second I ask some "Masters of the Internals" :
What is the reason for the false error message and where does it come from??

Winni

Oops: Lin64. fpc 3.04, Laz 2.0.10