Bug 8909 – Vertical scrollbar appears to detach during horizontal scrolling

• Status: NEW
• Component: Layout and Rendering

[David Kilzer (:ddkilzer)]

Summary: 

When a particular page loads, a vertical scrollbar is drawn and then later not needed, but it is never "undrawn" later (unless the window is resized or Safari is hidden and unhidden).  When the horizontal scrollbar is used, it appears to detach the vertical scrollbar that is no longer used.

Steps to Reproduce: 

1. Open Safari.
2. Load this URL:  http://www.zone-h.org/defacements/mirror/id=3680404/
3. If the vertical scrollbar is usable, click the "Reload" button once.

Expected Results: 

The vertical scrollbar should disappear after it is no longer being used.

Actual Results: 

The vertical scrollbar does not disappear after it is no longer being used.

Regression: 

This occurs in a local nightly build based on Subversion revision r14360.

It also occurs in Mac OS X 10.4.6 (Build 8I127) with Safari 2.0.3 (417.9.3).

Notes: 

This is bug is very timing-based during the page load.  Currently, about half of the page loads from the original web site cause this problem.

[David Kilzer (:ddkilzer)]

Created attachment 8306 [details]
Screenshot of detached scrollbar

[David Kilzer (:ddkilzer)]

Created attachment 8307 [details]
Movie of page loading and detached scrollbar

Note that the initial page load does not cause the problem, but the reload of the page does.

[David Kilzer (:ddkilzer)]

Created attachment 8309 [details]
Webarchive of problematic URL (does not exhibit the problem)

Note that the webarchive does not exhibit the problem since it is a timing issue.

[David Kilzer (:ddkilzer)]

Created Radar bug 4547726.  rdar://problem/4547726

[David Kilzer (:ddkilzer)]

(In reply to comment #0)
> 2. Load this URL:  http://www.zone-h.org/defacements/mirror/id=3680404/

The web site has been redesigned and the URL above no longer exists.  Hopefully there is enough information to recreate the problem using the webarchive.  Here is the new URL for the redesigned site (for what it's worth):

http://www.zone-h.org/index2.php?option=com_mirrorwrp&Itemid=43&id=3680404

[David Kilzer (:ddkilzer)]

Created attachment 8815 [details]
Partical reduction

This is a partial reduction of the problem.  The only external link left is the original <iframe> source.  I think it works well because it takes a while to load.  (For example, you could change the source to http://www.google.com/, but the problem doesn't reproduce as reliably.)

To reproduce the problem, shift-reload this page until the gray border at the bottom is fully visible, then scroll to the right.  The vertical scrollbar should appear to "detach", but is really just an artifact that should have been redrawn after it was no longer needed.

[David Kilzer (:ddkilzer)]

Mitz, I'm cc-ing you since I thought you'd get a kick out of the visual effects of this bug.

Maybe of interest: The description of a bug in Safari at the Ars Technica forum ( http://episteme.arstechnica.com/eve/forums?a=tpc&s=50009562&f=8300945231&m=869008469731&r=882003569731#882003569731 ) sounds very much like this one.

Created attachment 9073 [details]
Further reduction

It looks like the root cause is indeed a variation on bug 9531. The solution might be to take stronger action in the "view height changed" case added in that fix.

[David Kilzer (:ddkilzer)]

(In reply to comment #9)
> Created an attachment (id=9073) [edit]
> Further reduction
> 
> It looks like the root cause is indeed a variation on bug 9531. The solution
> might be to take stronger action in the "view height changed" case added in
> that fix.

I can't get this reduction to ever "detach" the vertical scroll bar (I'm still on 10.4.6 on PowerPC), but I suppose with a height of 100%, there shouldn't be a vertical scrollbar anyway.

(In reply to comment #10) 
> I can't get this reduction to ever "detach" the vertical scroll bar (I'm still
> on 10.4.6 on PowerPC), but I suppose with a height of 100%, there shouldn't be
> a vertical scrollbar anyway.
>  

Sorry. I should have clarified that the reduction is for that part of the bug. I'm going to try to add the second part, or better yet, a case that starts out with a legitimate vertical scrollbar.

Bug 11224 is the "horizontal scrollbar" version of this bug.

[Robert Hogan]

Can anyone still recreate this bug with any of the available reductions? I'm drawing a total blank - seems like there's nothing to do here anymore.

[Ahmad Saleem]

Using "Further Reduction" test case, I am getting same behavior across all browsers and they are showing horizontal scrollbar due to "1500 px" while it does not show vertical scrollbar. I tried resizing browser window to see if "vertical" scroll bar show up but it didn't.

I think I am not able to reproduce this in Safari 15.6.1, Firefox Nightly 106 and Chrome Canary 107.

If I am testing incorrectly, please update with updated test case. I will leave for others to comment on this and mark this bug accordingly. Thanks!