Nested boundaries often can't be selected

When I set a boundary around a branch and then set another boundary around a sub-branch, then sometimes I am unable to select that second nested boundary. If I hover and click on the nested boundary area I end up selecting the boundary of the parent branch instead of the nested boundary. It seems as if the nested boundary was created on a layer below the parent bound and I can't click on it or even hover over it. When this happens the only way to select the nested boundary is to first delete the parent boundary. 

This is a big problem because afaik there's no way to move focus onto a boundary using the keyboard. So it becomes impossible to change the style of these nested boundaries or even to delete them.

This bug seems to occur in about 20% of cases. The other times it works as I'd expect, i.e. boundaries applied to sub-branches receive focus priority over boundaries applied to parent branches. But I can't see any reason why the behaviour isn't consistent. 

Is there any solution or workaround for this?