backup path reset to defaul after restart joplin

[solarchen618]

Operating system

Windows

Joplin version

from 3.1.X to 3.2.1

Desktop version info

Joplin 3.2.1 (prod, win32)

Client ID: 019eebcd69324029b2e68b7ca3364876
Sync Version: 3
Profile Version: 47
Keychain Supported: Yes

Revision: cc87ece

Backup: 1.4.2
Draw.io: 2.2.0
Joplin Note Attachement rename: 1.2.2

Current behaviour

1.start joplin
2.change backup path in setting(for example, M:\joplinbackup)
3.start backup,and a backup zip file will showup in M:\joplinbackup
4.close joplin and restart
5.go to backup session of setting
6.the backup path reset to default (%PROFILE%/JoplinPortable/Data)
7.start backup again,a backup zip file will showup in %PROFILE%/JoplinPortable/Data rather in M:\joplinbackup

Expected behaviour

keeep backup path at M:\joplinbackup

Logs

No response

[solarchen618]

this happen in portable version.
and ,the synchronise path works fine.