2560941 - "Target System" of modifiable transport requests is blank after transport route was changed

You changed/re-configured transport route, after that, you found "Target System" of some modifiable transport requests became blank.
Also in transport route change log (Transport route screen -> Utilities -> display log -> Request Adjustments), you can see the following message:
Target of request XXX was changed from AAA to (blank).

Normally the message should be like:
Target of request XXX was changed from AAA to BBB.

Release independent

target system, target group, STMS, transport route, transport layer, target , KBA , BC-CTS-TMS , Transport Management System , BC-CTS-ORG , Workbench/Customizing Organizer , How To