Redmine

I an experiencing a weird issue with Redmine not accepting some certain text in the issue description. The server returns HTTP 504 both when I attempt to create a new issue, or to change the description of an existing one.
The problematic text is the following (JS code):

fail( function () {                                                 
    $('#workspace').removeSpinner();                                    
} );                                                                    

To reproduce the problem, simply copy-paste the above block of code to the description field of an issue in Redmine. It doesn't matter if the issue description contains only this block, or also some other text. It doesn't matter if the code is enclosed in <pre>..</pre> or not.

Nothing is written to the log after the message of a successful rendering of the page "/redmine/projects/viking/issues/new".

The following setup is used:

Environment:
  Redmine version                3.4.11.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.11.1
  Environment                    production
  Database adapter               PostgreSQL
SCM:
  Git                            2.7.4
  Filesystem                     
Redmine plugins:
  advanced_roadmap               0.11.0