Is this how it is suppose to work (on-demand issue) ?

So,  something odd happened the other day, and I am not sure if it is the way it works or not.

I was watching Terminator Genisys while it was live on some channel (I assume FX).  I  restarted the movie at the begining cause I missed a part (near as I could tell it was available on-demand),   Did not finish watching the movie,  exited the movie and wandered off.

Return to watch rest of the movie.  Used Last button which showed the movie with a resume under it.

Unable to resume the movie.  No longer in on-demand ?  See watch options to buy it or subscribe to FXM.  So what happened?  FX  put it in On-Demand while it was being broadcast live then pulled it after live broadcast ended?  Am I totally confused?

Ended up recording the next broadcast of the movie the next day and finished watching it a few days later so it is no problem, but I would like to understand what happened and how it is suppose to work.