Modification of a field by clicking on it - 404 error - undefined fields in POST request

[tkas]

When i try to edit a field (any) by clicking on it, change the value and then click to save it, it ends with a progress dialog forever. What happens is, that the server returns 404 error:

Started PUT "/redmine/spent_time" for XXX at 2015-11-05 09:50:30 +0100
Processing by SpentTimeController#index as JSON
Parameters: {"undefined"=>{"undefined"=>"Comment text"}, "authenticity_token"=>"xxxx"}
Current user: user (id=1)
Missing template, responding with 404
Completed 404 Not Found in 66.9ms (ActiveRecord: 0.0ms)

The problem is caused by sending wrong POST request to server, but I'm not sure who is responsible for constructing it.