It would appear that the default Idea Activity Story widget in 12.0.1.15778 is missing the same ContentPeek url formatting that other stories have by default.
Default:
#if ($content.Application.Container.ParentContainer)
<a href="$core_v2_encoding.HtmlAttributeEncode($content.Application.Container.Url)">$content.Application.Container.HtmlName('Web')</a>
<span class="group-application-separator">></span>
#end
<a href="$core_v2_encoding.HtmlAttributeEncode($content.Application.Url)">$content.Application.HtmlName('Web')</a>
Content Peek version:
#if ($content.Application.Container.ParentContainer)
<a $core_v2_ui.ContentPeek($content.Application.Container.ContainerId, $content.Application.Container.ContainerTypeId)
href="$core_v2_encoding.HtmlAttributeEncode($content.Application.Container.Url)">$content.Application.Container.HtmlName('Web')</a>
<span class="group-application-separator">></span>
#end
<a $core_v2_ui.ContentPeek($content.Application.ApplicationId, $content.Application.ApplicationTypeId)
href="$core_v2_encoding.HtmlAttributeEncode($content.Application.Url)">$content.Application.HtmlName('Web')</a>
