This is not a bug. It's simply "the way things work."
Lumetri is a standard effect. Speed effects are intrinsic (motion) effects. The two will cancel each other out because of something called the render order pipeline. All effects must follow a preset hierarchy. If you need certain effects to affect footage outside of this framework, you need to use an alternate method to do so.
The way editors create these effects is to use the method you discovered, or create the speed effect, nest the clip, then add the color effect to the nest. There are a number of effects you can create using this technique, so it's one you can place in your bag of tricks.
Please return with any questions you may have or mark this one as correct.
Hi, did you ever sort this out? I have the same issue and dont know a way around it. Im trying to simply colour grade the slowed down footage. Have tried method in reply but did not work. Perhaps I am doing it wrong. Any help would be much appreciated. Thanks