When you create a branch from Jira and select a "from branch" different from the default one, branch is still created from the default branch.
Thanks for contacting us. Unfortunately we could not reproduce the issue. The create branch functionality is working as expected.
We think, may be the confusion is from the "destination branch" displayed on the branch details page (the page you see after branch creation). The "destination branch" here does not indicate the branch from which it was created. (If you have branching model enabled for your repo, the destination branch will get selected based on the branch type.)