Some of my users report a strange keyboard problem where some of the buttons turn completely black (see the figure below). I install the keyboard on a dark keyboard in the AppDelegate of my application, and all the text fields are configured to use the default keyboard style. Has anyone else experienced this? Is this an iOS problem or something else in my application?

Edit:
This does not always happen. Only randomly. Here are my keyboard settings for this field (all other text fields correspond to these settings):

ios uikeyboard keyboard
Caseyc585
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