ROS Melodic + Ubuntu 18.04

I'm trying to build a workspace with both standard cmake and catkin packages using catkin_make_isolated. The catkin package builds successfully but the non-catkin package does not. It looks like catkin_make_isolated is calling make install even though I did not ask for an install. I don't have an install target for the non-catkin package.

The non-catkin package does have a package.xml with

<export>
    <build_type>cmake</build_type>
</export>

Here's the relevant portion of the output.

==> Processing plain cmake package: 'smallproject'
==> Creating build directory: 'build_isolated/smallproject/devel'
==> Building with env: '/home/myuser/smallproject/devel_isolated/example_pkg/env.sh'
==> cmake /home/myuser/smallproject/src/smallproject/smallproject -DCMAKE_INSTALL_PREFIX=/home/myuser/smallproject/devel_isolated/smallproject -G Unix Makefiles in '/home/myuser/smallproject/build_isolated/smallproject/devel'
-- The CXX compiler identification is GNU 7.3.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Conan: checking conan executable in path
-- Conan: Found program /home/myuser/.local/bin/conan
-- Conan: Version found Conan version 1.13.1

-- Conan: Adding bincrafters remote repositoy (https://api.bintray.com/conan/bincrafters/public-conan)
-- Conan: Automatic detection of conan settings from cmake
-- Conan: Settings= -s;build_type=Release;-s;compiler=gcc;-s;compiler.version=7;-s;compiler.libcxx=libstdc++11
-- Conan executing: conan install /home/myuser/smallproject/src/smallproject/smallproject/conanfile.txt -s build_type=Release -s compiler=gcc -s compiler.version=7 -s compiler.libcxx=libstdc++11 -g=cmake --build=missing
-- Configuration:
[settings]
arch=x86_64
arch_build=x86_64
build_type=Release
compiler=gcc
compiler.libcxx=libstdc++11
compiler.version=7
os=Linux
os_build=Linux
[options]
[build_requires]
[env]

conanfile.txt: Installing package
Requirements
    eigen/3.3.7@conan/stable from 'conan-center' - Cache
Packages
    eigen/3.3.7@conan/stable:5ab84d6acfe1f23c4fae0ab88f26e3a396351ac9 - Cache

eigen/3.3.7@conan/stable: Already installed!
conanfile.txt: Generator cmake_find_package created Findeigen.cmake
conanfile.txt: Generator cmake_paths created conan_paths.cmake
conanfile.txt: Generator cmake created conanbuildinfo.cmake
conanfile.txt: Generator txt created conanbuildinfo.txt
conanfile.txt: Generated conaninfo.txt
conanfile.txt: Generated graphinfo

-- Conan: Loading conanbuildinfo.cmake
-- Current conanbuildinfo.cmake directory: /home/myuser/smallproject/build_isolated/smallproject/devel
-- Conan: Compiler GCC>=5, checking major version 7
-- Conan: Checking correct version: 7
-- Conan: Using cmake targets configuration
-- Conan: Adjusting default RPATHs Conan policies
-- Conan: Adjusting language standard
-- Conan: Using autogenerated Findeigen.cmake
-- Found eigen: 3.3.7 (found version "3.3.7") 
-- 
-- SmallProject
-- Project Dir: /home/myuser/smallproject/src/smallproject/smallproject
-- Binary Dir:  /home/myuser/smallproject/build_isolated/smallproject/devel
-- Build Type:  Release
-- Testing:     ON
-- Libraries:   example_lib
-- CCache:      /usr/bin/ccache
-- 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/myuser/smallproject/build_isolated/smallproject/devel
==> make -j4 -l4 in '/home/myuser/smallproject/build_isolated/smallproject/devel'
Scanning dependencies of target example_lib
[ 20%] Building CXX object lib/example_lib/CMakeFiles/example_lib.dir/src/example_lib.cpp.o
[ 40%] Linking CXX static library ../libexample_lib.a
[ 40%] Built target example_lib
Scanning dependencies of target test_example_lib
[ 60%] Building CXX object test/example_lib/CMakeFiles/test_example_lib.dir/__/test_main.cpp.o
[ 80%] Building CXX object test/example_lib/CMakeFiles/test_example_lib.dir/test_example_lib.cpp.o
[100%] Linking CXX executable ../../bin/test_example_lib
[100%] Built target test_example_lib
==> make install in '/home/myuser/smallproject/build_isolated/smallproject/devel'
make: *** No rule to make target 'install'.  Stop.
<== Failed to process package 'smallproject': 
  Command '['/home/myuser/smallproject/devel_isolated/example_pkg/env.sh', 'make', 'install']' returned non-zero exit status 2

Reproduce this error by running:
==> cd /home/myuser/smallproject/build_isolated/smallproject && /home/myuser/smallproject/devel_isolated/example_pkg/env.sh make install

Command failed, exiting.

A similar thing happens if I try using catkin build from catkin_tools.

Any ideas?

Thanks!