On touch devices the HTML5 client runs in panning mode. This means that if the remote session is larger than the viewport, you get the option to pan (the hand icon). Currently, you cannot click while panning, you have to toggle it off before clicking.
Users who are using the HTML5 client on a device with a small screen or low resolution will be using panning mode a lot. The toggling back and forth is annoying. We should make it possible to click while panning.
Work on this is being done upstream:
There is an issue on some devices that causes problems. Due to this, the changes include an added 10 px threshold for panning (you have to move more than 10 px before it starts panning).
Fixed now with the vendordrop that was made for bug 5814.
To test this, the tester should use a touch device. In order to enable panning you can run xrandr to set a higher resolution (it will automatically resize when you for example rotate the device).
Tested on CentOS 7 and Safari on iOS/iPhone6. could click, like closing windows without leaving panning mode.