Cannot enter upon force-push if repository has a submodule

Steps to reproduce

1. On GitHub, create two private repositories named "repo1" and "repo2" with "Initialize this repository with a README" enabled
2. On SourceTree, open new tab and...
   1. Select "Clone" icon
   2. Enter https://github.com/<account>/repo1.git to "Source Path / URL:"
   3. Enter C:\test\repo1 to "Destination Path:"
   4. "Clone" and wait
   5. Click "Remote" icon with a red exclamation mark
   6. "Settings" -> Double-click "origin" line -> "OK" to close remote details -> "OK" to close repository settings
   7. Confirm the exclamation is removed
      • So steps 2-5 ~ 2-7 are just for calming it
3. Open new tab and do same except its url/path/name is for repo2
4. On SourceTree repo1 tab, right-click the left panel and select "Add Submodule..."
5. Enter https://github.com/<account>/repo2.git to "Source Path / URL:" -> "OK"
6. "Stage All" and commit with "Push changes immediately to origin/master" enabled
7. On local repo1 directory, create "textA.txt"
8. On SourceTree repo1 tab, "Stage All" and commit with "Push changes immediately to origin/master" enabled
9. Right-click on the second commit (the one when added submodule) and select "Reset current branch to this commit" -> select "Hard" -> "Yes" and confirm "textA.txt" is removed from local repo1
10. On local repo1 directory, create "textB.txt"
11. On SourceTree repo1 tab, "Stage All" and just commit without "Push changes immediately to origin/master" enabled
    • Now the master shows "1↑ 1↓" state
12. Select "Push" icon to show push screen
13. "Push" master
14. Confirm Sourcetree shows error, of cause, then close
15. Push again with "Force Push" enabled
    • No matter if "Use Safe Force Push" is enabled in SourceTree preference

Expected behavior

• Succeed force-push, or get another error at least

Actual behavior

• Sourcetree shows "Submodule Check" dialog for a split second and returns to push screen (step 12) automatically at once

Handy solution (for users)

1. Just push without "Force Push" checked and confirm the error appears
2. Copy the first line (Git command) from the error and close
3. "Cancel" to close push screen
4. Select "Terminal" icon
5. Paste the command on terminal, insert "-f" option manually and press enter key
   • My case:

     git -c diff.mnemonicprefix=false -c core.quotepath=false --no-optional-locks -c credential.helper= -c credential.helper="C:/Users/<user>/AppData/Local/ATLASS~1/SOURCE~1/GIT_EX~1/GIT-CR~1.EXE" push -f -v origin master:master

1. Wait to confirm success and close terminal