Repro Steps:

1) Create a Page
2) Using the Path Tool (P), draw 3 overlapping, fully enclosed shapes within the Page's RootGrid. Please ensure these are 3 different Paths, and not 3 PathFigures within a single Path.
3) Name the visually bottom-most layer to a custom name (aka the layer closest to the RootGrid)
4) Hold [Ctrl], and in the Navigator, click on all 3 Paths to multi-select them, ensuring to start with the layer with the custom name.
5) Once all 3 layers are selected, right-click on any of them, and from the context menu, navigate to 'Path', then 'Unite'. At this point, you will see that two of the three Paths have been united.
6) Press [Ctrl+Z] to undo the Booleaning. At this point you will see that the layer that used to have a custom name, has lost it and has been renamed to 'Path'.

7) Hold [Ctrl], and in the Navigator, click on the first two Paths to multi-select them, ensuring to start with the layer that used to have the custom name.
8) With both layers selected right-click on any of them, and from the context menu, navigate to 'Path', then 'Unite'.

Observe how the new compound path is assigned the name that the defunct custom layer name used to have.

Expected Results: Layer Names are not lost in an Undo operation (Step 6)).
Expected Results: Layer Names are given to new compound Paths, are those of the 'master' (ie the layer that the Boolean action was triggered from)