I have the same issue on a Samsung Galaxy S5. Phone is about 2 months old from AT&T.
Sometimes,when I hit the microphone icon on the Samsung keyboard (say, for texting), the Tap to Speak screen allows me to, well, tap and speak at first, then it goes inactive (button turns white) and I cannot close it out by any means. All functions on that screen go dead and the screen sits there on top of everything but the lock screen. If I rotate the screen to landscape, the Tap to Speak screen slides off the bottom, but if I rotate back to portrait, the Tap to Speak screen slides back up.
If I restart or power off/on the phone, the Tap to Speak screen is gone.
I am unable to attribute the issue beginning with any updates or changes, but I'm sure I did something. :-\