trigger phrase not building the jenkins job if target branch is modified

[DilshadPt]

Hello Team,

ghrb version 1.33.1
jenkins version 2.7.4

I have a jenkins job which watches PR raised to a specific whitelisted target branch. I use ghprb for triggering builds for PR.
I use 'Whitelist target branch' for filtering PR 's to our default branch and trigger phrase for building the job.

Recently I saw this happening.
Steps:

1. A PR raised with base branch as another branch (not whitelisted branch)
2. commented the PR with trigger phrase and it didn't build the job as expected.
3. PR was updated/modified with base branch as whitelisted branch
4. commented the PR with trigger phrase, but job was not triggering. I tried commenting multiple times and tested the same on two PRs. But the job was not triggered.

I had to raise a new / duplicate PR with base branch as whitelisted branch to get it working.

Is this an expected behaviour or a bug ?

Thanks in Advance.