Hello. I'm Dale, the test engineer at Dropsource. I was able to reproduce the issue you reported regarding an image view element overlaying a text button element. I forwarded my findings to our development team and they are looking into the issue.
In the meantime, I tested some different alternatives to get you around the issue and found that the same issue does not occur if you have an image view overlaying an image button (instead of a text button).
Instead of overlaying an image over a text button, you could try to flip it around by overlaying a text view over an image button to achieve a similar effect of combined image and text on a button. I have verified that this does not experience the same issue.
I will let you know the results of our findings, but see if the text view over the image button will work for your case.