Trouble with the right value for HeaderFilterRegex

Hi,

I can't get HeaderFilterRegex to work. It always expands to the build path where the compile commands are. What's the error?

My parameters are:

"c:\Program Files\LLVM\bin\clang-tidy.exe" --version
LLVM (http://llvm.org/):
LLVM version 7.0.1
Optimized build.
Default target: x86_64-pc-win32
Host CPU: haswell

CMake based project in "c:\Project" which is build in "c:\Build". The .clang-tidy file is in "c:\Project".

If I run

c:\Python\python37\python.exe "c:\Program Files\LLVM\share\clang\run-clang-tidy.py" -clang-tidy-binary "c:\Program Files\LLVM\bin\clang-tidy.exe" -p c:\Build

(inside c:\Project) I always get

c:\Program Files\LLVM\bin\clang-tidy.exe -header-filter=^c:\Build/.* ...

regardless which value I try in HeaderFilterRegex. Examples

HeaderFilterRegex: '.*'
HeaderFilterRegex: 'Common/.*'

By altering the "Checks" at the .clang-tidy file I had make sure it is actually loaded.

What I want is that HeaderFilterRegex expands to "c:\Program Files\LLVM\bin\clang-tidy.exe -header-filter=Common/.*".
(If I explicitly call

c:\Python\python37\python.exe "c:\Program Files\LLVM\share\clang\run-clang-tidy.py" -clang-tidy-binary "c:\Program Files\LLVM\bin\clang-tidy.exe" -p c:\Build -header-filter=Common/.*

it behaves how I want it to.)

So, can you give me a hint what I am doing wrong? What value must HeaderFilterRegex have?

Thanks
Sebastian