Resolve the conflicts did not show the merge_head with correct branch name

What steps will reproduce the problem?

C1<--C2
<--C3

1. have three branches, branchA and branchB and branchC
2. branchA point to C2, branchB also point to C2, and branchA was created before branchB
3. branchC point to C3
4. C1 is the common parent of C2 and C3
5. switch to branchC, and merge branchB

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

The merge_head should be branchB, but TortoiseGit shows merge_head with branchA
And I expect TortoiseGit to show merge_head and head both with commit id

What version of TortoiseGit and Git are you using? On what operating system?
TortoiseGit 2.11.0.0 (C:\Program Files\TortoiseGit\bin)
git version 2.29.2.windows.2 (C:\Program Files\Git\bin; C:\Program Files\Git\mingw64; C:\Program Files\Git\etc\gitconfig)
Win10