Bug Using Kivy with a Waveshare Resistive Touchscreen

[Daniel1]

I have noticed a very strange bug using kivy with the following touchscreen for the raspberry pi - https://www.waveshare.com/wiki/5inch_HDMI_LCD_(B).

Once the touchscreen is calibrated and the relevant adjustments made to the kivy config, the screen is suitably responsive to touches in most cases. The exception is when a popup is open, particularly the VKeyboard, where touches are very hard to register - it often requires several touches or a press and hold before a button press is registered. This is substantially different to when a popup is not present, in which case the slightest tap is easily registered.

Does anyone have the slightest idea how/why the responsiveness varies in this manner?