Commit message autocompletion bugs out after typing a second character

What steps will reproduce the problem?

1. Open the commit dialog and start typing a commit message
2. Have several entries starting with the same letter (i.e. "M") in the autocompletion dropdown:
3. Type M (autocomplete dropdown appears)
4. Type e (autocomplete dropdown disappears and won't reappear even on CTRL+Space, unless the word is trimmed down to a single "M")

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

I would hope that typing Me would filter the autocomplete dropdown to "MergeLeistungsbringer" instead of nothing, but that clearly isn't happening... :(

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

TortoiseGit 2.3.0.0 (C:\Devel\TortoiseGit\bin)
git version 2.10.0.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.

The files are using UTF-8 encoding with a BOM.