Customizer: interacting with text fields in a "wide" widget shifts child panel position in Safari.

[pagelab]

When a widget is defined as "wide" in the widget construct, there's a sudden shift of the "widgets" panel in the customizer when there's any interaction with a text field.

This was observed in Safari Mac, versions 11 and 13 (latest).

I've used WordPress 4.9-beta3-41983, but this happened also in 4.8.2.

This bug was detected while I was using the Black Studio TinyMCE Widget plugin: ​https://br.wordpress.org/plugins/black-studio-tinymce-widget/.

I have tested also with a simple widget plugin, and found the same bug.

On both WordPress installations, the Twenty Seventeen theme was active, and there was just two plugins active: the test widget plugin and Black Studio TinyMCE Widget plugin.

• Here's a video showing the bug: ​https://www.dropbox.com/preview/Screen-Recording-2017-10-24-20-39-12.mp4?share=1
• The widget plugin used in the test is here: ​https://dl.dropbox.com/s/thmywibr3fd2d1x/widget-test.php.zip

[pagelab]

Simple widget plugin to test the bug.

[westonruter]

@pagelab I wasn't able to access your video on Dropbox, so I uploaded a video for myself: ​https://youtu.be/h13gfRdszIs

This issue was also happening in the new theme browser: #42052. In particular, it was fixed by @sayedwp in [41948].

But I found that if I go back to WordPress 4.7 the issue is still present there, so it's not new in 4.9. It is probably a regression introduced in #34391.