Cancel button do not work in conflict dialog when uploading files to a DropBox mount

[davitol]

Steps to reproduce

0. Enable Dropbox app. (release/1.1.0).
1. Set up Dropbox mount point, grant access and so on. (all ok).
2. Upload a file via WebUI called test.txt
3. Try to Upload a file via WebUI called Test.txt
4. Try to cancel the Pop up Dialog

Expected behaviour

The pop up should be closed and no action should happen over test.txt file

Actual behaviour

Cancel button do not work. If you select other option a warning appears and a log is spotted in owncloud.log

Server configuration

Operating system:
Ubuntu 16.04

Web server:
Apache

PHP version:
7.2

Cache
DB

ownCloud version: (see ownCloud admin page)

ownCloud 10.0.10

Updated from an older ownCloud or fresh install:
Fresh

The content of config/config.php:

Are you using external storage, if yes which one: local/smb/sftp/...
Yes, dropbox.

Are you using encryption:
No.

Logs

{"reqId":"EVV7bC0YVBi8Kv0ygZbG","level":4,"time":"2018-12-14T10:06:06+00:00","remoteAddr":"85.57.168.79","user":"admin","app":"webdav","method":"PUT","url":"\/owncloud\/remote.php\/webdav\/DropboxV21\/historial.txt","message":"Exception: HTTP\/1.1 500 Could not rename part file to final file: {\"Exception\":\"Sabre\\\\DAV\\\\Exception\",\"Message\":\"Could not rename part file to final file\",\"Code\":0,\"Trace\":\"#0 \\\/var\\\/www\\\/html\\\/owncloud\\\/lib\\\/composer\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Server.php(1129): OCA\\\\DAV\\\\Connector\\\\Sabre\\\\File->put(Resource id #73)\\n#1 \\\/var\\\/www\\\/html\\\/owncloud\\\/lib\\\/composer\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/CorePlugin.php(513): Sabre\\\\DAV\\\\Server->updateFile('DropboxV21\\\/hist...', Resource id #73, NULL)\\n#2 [internal function]: Sabre\\\\DAV\\\\CorePlugin->httpPut(Object(Sabre\\\\HTTP\\\\Request), Object(Sabre\\\\HTTP\\\\Response))\\n#3 \\\/var\\\/www\\\/html\\\/owncloud\\\/lib\\\/composer\\\/sabre\\\/event\\\/lib\\\/EventEmitterTrait.php(105): call_user_func_array(Array, Array)\\n#4 \\\/var\\\/www\\\/html\\\/owncloud\\\/lib\\\/composer\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Server.php(479): Sabre\\\\Event\\\\EventEmitter->emit('method:PUT', Array)\\n#5 \\\/var\\\/www\\\/html\\\/owncloud\\\/lib\\\/composer\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Server.php(254): Sabre\\\\DAV\\\\Server->invokeMethod(Object(Sabre\\\\HTTP\\\\Request), Object(Sabre\\\\HTTP\\\\Response))\\n#6 \\\/var\\\/www\\\/html\\\/owncloud\\\/apps\\\/dav\\\/appinfo\\\/v1\\\/webdav.php(64): Sabre\\\\DAV\\\\Server->exec()\\n#7 \\\/var\\\/www\\\/html\\\/owncloud\\\/remote.php(165): require_once('\\\/var\\\/www\\\/html\\\/o...')\\n#8 {main}\",\"File\":\"\\\/var\\\/www\\\/html\\\/owncloud\\\/apps\\\/dav\\\/lib\\\/Connector\\\/Sabre\\\/File.php\",\"Line\":267}"}

Client configuration

Browser
Firefox