The bug fixed in EPiServer.CMS.UI 12.19.0 (CMS-27369) still appears to not work for CollectionEditorDescriptor.

Here's a trimmed snippet that should illustrate the problem:

    [ContentType(DisplayName = "Bar Chart")]
    public class BarChartBlock : BlockData
    {
        [CultureSpecific]
        [Display(Name = "Title", GroupName = SystemTabNames.Content, Order = 10)]
        public virtual string Title { get; set; }

        [CultureSpecific]
        [Display(Name = "Data Labels", GroupName = SystemTabNames.Content, Order = 20)]
        public virtual IList<string> DataLabels { get; set; }

        [CultureSpecific]
        [Display(Name = "Data Sets", GroupName = SystemTabNames.Content, Order = 30)]
        [EditorDescriptor(EditorDescriptorType = typeof(CollectionEditorDescriptor<BarChartDataSet>))]
        public virtual IList<BarChartDataSet> DataSets { get; set; }
    }

    public class BarChartDataSet
    {
        [CultureSpecific]
        [Required]
        [Display(Name = "Label", GroupName = SystemTabNames.Content, Order = 10)]
        public virtual string Label { get; set; }

        [Display(Name = "Values", GroupName = SystemTabNames.Content, Order = 20)]
        public virtual IList<string> Values { get; set; }
    }

    [PropertyDefinitionTypePlugIn(DisplayName = "Bar Chart Data Set")]
    public class BarChartDataSetProperty : PropertyList<BarChartDataSet> { }

The Item Details modal currently still shows Values as a textarea: