The way redo select base directory confuses?

[Zhonghua Mo]

For example, I have a project located at  /home/mzh/projects/foobar, I build it with following commands:

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cd /home/mzh/projects/foobar

redo all

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What confusing me is that redo don't select base directory to create .redo consistently:

1. if there is no .redo in current directory but a .redo in one parent directory of /home/mzh/projects/foobar, then the parent directory is used as base

2. if there is no .redo in current directory and in any parent directory, then curent diretory, i.e. ,/home/mzh/projects/foobar is used as base, and create .redo in current directory

3. if there is a .redo in current directory and .redo in one parent diretory, then _parent directory_ is used as base

I think redo should use current diretory as base in case 3. Or is there any reason to select parent directory as base deliberately in case 3?