Filename autocomplete in commit dialog ignores filenames starting with underscores

What steps will reproduce the problem?

1. Create files with names like "_MitarbeiterEdit.cshtml", "_MitarbeiterDisplay.cshtml" (filename convention for partial views in ASP.Net MVC)
2. Write a commit message and type "_M"

What is the expected output? What do you see instead?

Expected: autocomplete dropdown should include changed file "_MitarbeiterEdit.cshtml"
Actual: autocomplete dropdown doesn't trigger on "_", and neither on Ctrl + Space afterwards, but if I start typing the full pathname the dropdown includes the file with it's full path (i.e. "eCS.Projectname/Views/Kontakt/_MitarbeiterEdit.cshtml"

What version of TortoiseGit and Git are you using? On what operating system?

TortoiseGit 2.5.0.0 (C:\Devel\TortoiseGit\bin) git version 2.13.3.windows.1 (C:\Devel\Git\bin; C:\Devel\Git\mingw64; C:\Devel\Git\mingw64\etc\gitconfig; C:\ProgramData\Git\config)

Please provide any additional information below.

Turning off "StyleCommitMessages" in the advanced TortoiseGit settings makes these files appear in the dropdown, but at least when triggering the dropdown with Ctrl + Space after and underscore I'd expect the files to be there, "StyleCommitMessages" or not...