Unable to display task with task input equal to constant

It is not possible to display a task with task input equal to constant with business-central. It ends with error:

{"ToSubject":"org.jbpm.workbench.ht.service.TaskService:RPC.getTask:java.lang.String:java.lang.String:java.lang.Long::128:RespondTo:RPC"}

| Uncaught exception: Client-side exception occurred although RPC call succeeded. Caused by: (TypeError) : Cannot read property 'h' of undefined

For testing purposes, we have used Integer task input variable, and constant '2'

KJAR is attached - simply deploy it onto kie-server, start the VarERROR and VarOK process and try to display both tasks from inside business-central (i.e. Task Inbox)

Task from VarOK is using variable mapping and it gets displayed OK
Task from VarERROR is using constant as a task input and won't get displayed