closes #2251 thanks to @rsbondi patch

lib/browser/tag/tag.js

@@ -114,8 +114,8 @@ export default function Tag(impl = {}, conf = {}, innerHTML) {
   // create a unique id to this tag
   // it could be handy to use it also to improve the virtual dom rendering speed
   defineProperty(this, '_riot_id', ++__uid) // base 1 allows test !t._riot_id
-
-  extend(this, { root, opts }, item)
+  defineProperty(this, 'root', root)
+  extend(this, { opts }, item)
   // protect the "tags" and "refs" property from being overridden
   defineProperty(this, 'parent', parent || null)
   defineProperty(this, 'tags', {})

lib/browser/tag/update.js

@@ -1,7 +1,7 @@
 import { tmpl } from 'riot-tmpl'
 import { startsWith, each, contains } from './../common/util/misc'
 import { isFunction, isUndefined } from './../common/util/check'
-import { remAttr, setAttr, createDOMPlaceholder } from './../common/util/dom'
+import { remAttr, getAttr, setAttr, createDOMPlaceholder } from './../common/util/dom'
 import setEventHandler from './setEventHandler'
 import {
   initChildTag,
@@ -75,6 +75,8 @@ export function updateDataIs(expr, parent) {
  * @returns { undefined }
  */
 export function updateExpression(expr) {
+  if (this.root && getAttr(this.root,'virtualized')) return
+
   var dom = expr.dom,
     attrName = expr.attr,
     isToggle = contains([SHOW_DIRECTIVE, HIDE_DIRECTIVE], attrName),

test/specs/browser/core.spec.js

@@ -33,6 +33,7 @@ import '../../tag/runtime-event-listener-switch.tag'
 import '../../tag/should-update.tag'
 import '../../tag/observable-attr.tag'
 import '../../tag/virtual-nested-unmount.tag'
+import '../../tag/virtual-conditional.tag'
 import '../../tag/form-controls.tag'
 import '../../tag/data-is.tag'
 import '../../tag/virtual-nested-component.tag'
@@ -1182,4 +1183,22 @@ describe('Riot core', function() {
     tag.unmount()
   })
 
+  it('virtual tags with conditional will mount their children tags properly', function() {
+    injectHTML('<virtual-conditional></virtual-conditional')
+    var tag = riot.mount('virtual-conditional')[0]
+
+    riot.util.tmpl.errorHandler = function () {
+      throw new Error('It should render without errors')
+    }
+
+    expect(tag.childMountCount).to.be.equal(0)
+    tag.user = { name: 'foo' }
+
+    tag.update()
+    expect(tag.childMountCount).to.be.equal(1)
+
+    riot.util.tmpl.errorHandler = null
+
+  })
+
 })

test/tag/virtual-conditional.tag

@@ -0,0 +1,21 @@
+<virtual-conditional>
+  <virtual if={ user != null }>
+    <p>{ user.name }</p>
+    <virtual-conditional-child></virtual-conditional-child>
+  </virtual>
+
+  <script>
+    this.childMountCount = 0
+    this.user = null
+  </script>
+</virtual-conditional>
+
+<virtual-conditional-child>
+  <p>hi</p>
+
+  <script>
+    this.on('mount', function() {
+      this.parent.childMountCount ++
+    })
+  </script>
+</virtual-conditional-child>