When changing the Web Access appearance in bug 7908, we removed the -webkit-tap-highlight-color. This causes Safari on iOS to no longer give any visual feedback when pressing buttons. This behaviour is a regression compared to 4.14.0.
Our buttons have :active styling, which works on other platforms as well as other browsers in Safari.
The problem does not occur when using a trackpad on iOS.
Note that this visual bug only occurs if there is no event listener on any outer element from the button or the button itself. E.g., for the buttons in the sidebar and "extra keys" (shown when logged in to webaccess), a press is shown just fine since they have an event listener that makes the sidebar fade when inactive.
A solution that has been recommended by Apple is using 'ontouchstart' with an empty value just to get an event listener attached to the object, see:
Another solution is to set 'ontouchstart' on the body element itself, but this feels a bit more hacky:
Both these methods successfully makes the button give visual feedback when pressed.
Here is a webkit bug for this:
Note that it was reported 2014 and there are no clear indications if this will ever be fixed.