Ranges for consecutive citations does not work when using prefix


I am using Endnote style TF-Standard NLM and have checked the box Citations - Numbering - Use ranges for consecutive citations. This works when I have three or more citations (such as: 1-3) but as soon as I use a prefix before the first author Endnote reverts this setting back to: e.g. 1,2,3. Is that a bug?