Confusion about text box

[Francis22422790ddg4]

I've been given a document to edit. It has two columns and many pages, all threaded together. The columns are fit to the margins and gutter. The text  usually flows normally, but in a few columns the text box is push down and there is a half, or on some instances, an entire line into the bottom margin. When I add text, it occassionaly does the same thing - push the text box down into the margin. 

I'm thoroughly confused. I thought that the text box restricts where text can appear, yet adding text seems to cause it to expand in some cases but not in others. What is going on here? How can I stop it?

[Steve Werner]

Different things can affect text flow and we could use more information to help. Please turn on Normal view and Show Hidden Characters. Select the text frame and make a screen capture. Upload it with the Insert Photos button.

[Willi Adelberger]

Look into the object style. There could be the possibility to fit size to  content.