CMake linking error at runtime from other lib in subdirectory - cmake

Question

I am trying to get a project running that is using dynamic openCASCADE libraries.
So first i set up a minimal test project using the following CMake file:
...
include_directories(/home/user/occt/build_r/include/opencascade/)
add_executable(testOCCT
main.cpp
step2stl.cpp
)
find_package(OpenCASCADE REQUIRED NO_DEFAULT_PATH)
set(OCCT_LIBS TKMesh; TKSTEP; TKSTL; TKXSBase; TKernel)
target_link_libraries(testOCCT ${OCCT_LIBS})
This is working as it should.
Now i want to link the same libraries to another library that is used in a larger project.
For the project there are 3 CMake files, one for the project and two subdirectory, one for the executable one for the myLib, which are added by add_subdirectory().
In the CMake file for myLib which is inside one of the subdirectories I've added:
...
include_directories(/home/user/occt/build_r/include/opencascade/)
...
add_library(${MY_LIB_NAME} SHARED ${my_sources})
find_package(OpenCASCADE REQUIRED NO_DEFAULT_PATH)
set(OCCT_LIBS TKMesh; TKSTEP; TKSTL; TKXSBase; TKernel)
target_link_libraries(${MY_LIB_NAME} ${OCCT_LIBS})
so basically the same as in the test project.
However now I get an error (at runtime):
symbol lookup error: myLib.so: undefined symbol: _ZN24BRepMesh_IncrementalMeshC1ERK12TopoDS_Shapedbdb

Answer 1

Ok, so i found the problem myself. The reason it did not work was not because of CMake, but that there was some other version of the libraries installed over the packet manager, which then got loaded instead of the right one.
purging those libs solved the problem.
However what I still don't get is why it loaded the correct library version on the test project and the wrong on the other (both tested on the same machine)