Still can scroll parent elements by dragging &dropping scrollbar after an element is locked

[vincentcn]

Should be an issue for iron-scroll-manager.js.
After locking an element by calling pushScrollLock from iron-scroll-manager.js, the scroll on locked element's parent elements are expected to be locked.

You do cannot scroll them by mouse wheel or trackpad, but still can scroll them by dragging &dropping scrollbar.(You may need set "show scroll bars" to "always" in system preferences to reproduce it on mac.)

Expected outcome

Cannot scroll the locked element's parent elements.

Actual outcome

The locked element's parent elements still can be scrolled by dragging &dropping scrollbar.

Live Demo

Browsers Affected

• Chrome
• Firefox
• Safari 9
• Safari 8
• Safari 7
• Edge
• IE 11
• IE 10

[vincentcn]

Anyone can help to check this issue? @bicknellr ?