Bug 171030 – CSS transition delayed for elements transitioning text properties

• Component: Animations
• Status: NEW

Created attachment 307540 [details]
Initial demo of bug (bugged in WebKit, works in FireFox)

When using jQuery to toggle a class for an element (activated by clicking anywhere in the JSFiddle), certain conditions will cause the timing of a CSS transition to be delayed.

In the attached demo (https://jsfiddle.net/sowteck9/4/), the <p>'s should transition together and immediately.

However, the second <p>'s transition is delayed. Commenting out the styling for .first or setting all values to a default value (i.e. inherit, 1em, currentColor, normal, etc.) will cause both <p>'s to be delayed by 1s. The same thing happens with any font-relative length value besides rem (i.e. em, ex, ch, ic, lh, rlh) the property font-size. Commenting out the inner <div> (but not its inner HTML) will cause the bug to not reproduce either.

I have tried the CSS properties color, font-size, letter-spacing, and opacity. Opacity does not trigger the bug, which makes me think that it might be specific to text properties.

I have not tried using vanilla JavaScript (as opposed to jQuery) to reproduce the bug yet.

This bug occurs in Chrome 58.0.3029.81 (64-bit), Safari 10.1 (12603.1.30.0.34), WebKit 10.1 (12603.1.30.0.34, r215523), and Opera 44.0.2510.1218. This bug does not occur in Firefox 53.0. These browsers were run on macOS Sierra 10.12.4 64-bit.

[Simon Fraser (smfr)]

I think we have another bug on this same issue.

[Antoine Quint]

We behave the same as Chrome here, but Firefox animates both <p> together.