Read-only integer custom work-item field problem

Hello,

I've defined a customer work item field that is of type integer and uses an editor presentation of integer. I would like it to:
- be displayed only if non-null
- to be read-only in the work item editor

I've added the key-value pairs for the editor presentation:
readonly,true
hideIfEmpty,true

The "hideIfEmpty" works fine. However the readonly key doesn't - the editor displays it as a regular integer field and it can be edited and saved (both in RTC client and browser interfaces).

Anyone have any suggestions for resolving this please?