I brought up a similar issue yesterday. I have a simple, 2-column text box. I want the last two of five lines to be in the second column. No matter what I do, those lines won't go over. In Story Edit mode, the two lines show as overset. This is nuts, really nuts. And, I've only seen this behavior since I updated to 2015 last week. Yesterday I had a similar issue, where the box was showing overset text, even though it still had at least an inch of vertical space for more type. I only, finally, discovered that there was indeed some text in there, in the Story Editor. But, it's still not making sense to me.
The best way to diagnose this problem is going to be to select the first line of overset text in story editor and look at the attributes. Might be a Keep option to start in next frame or on next page.
If this file started in an earlier version, see Remove minor corruption by exporting. There are so many reports of direct conversion glitches now that I no longer even attempt it. If I have to convert I always export to IDML from the original version and convert that.
Thanks. Yeh, I see "keep with next (1) line" in there. That's all. I've just gone ahead and made two separate columns.
I created this ID file in ID 2015, nothing earlier.