Text disappears after scrolling off-screen

Okay, so I created some text that I'd like to scroll horizontally, from right to left, beginning off-screen on the right and ending up off-screen on the left.

I've done this before successfully, but today it's not working.  When I drag the off-screen text back on-screen, the previously off-screen portion of the text has disappeared, as if cropped off and deleted.

Example.

1) I position text such as, "Hello there" at the edge of screen so that only the "H" is visible.

2) I set keyframes to record this original position.

3) I drag the first positioning value so that the text "Hello there" will move left (until I find the new location where I would like the text to end up).

But as I drag "Hello there" to the left like this, only the "H" appears.  The rest of the text has been cut off or masked somehow.  I don't think it's just masked, however, because I can drag the "H" anywhere and it continues to appear by itself.

I'm baffled because I have employed no other effect that should interfere with the text.  I have deleted the text segment and re-created it.  Still, the same thing happens.  I drag all but the first letter off-screen to the right and set key frames.  But then when I attempt to relocate entire text to the left, I see while dragging that the text has been cannibalized -- the portion of the text that was hiding off-screen is now no longer part of the text.