This is a known issue and it will be worked on soon. There is a conversation related to this on T251590: Inline FieldLayout isn't inline when it contains a TextInputWidget.

Update: We are resolving this issue for now via T260759. If the issues brought up in T251590 are later addressed, we can look into later adding in the label into the legacy source editor again. However, in the interest of keeping the project within scope and on schedule, we will be focusing on removing the label as a solution for now. I'm merging this task with T260759. Thanks!