Why does my frame range start automatically revert back to 0 after I set it? I want to do as described here: How Do You Start Animation At A Specific Frame?

Whether I use the setter below the timeline, or the one in the render panel, immediately after I set it--clicking anywhere else--it goes back to 0.  Also trying to set it via the arrows, you can't get past 1, and that also reverts to 0 as soon as you click elsewhere.  Even if I type it in the render panel and the next thing I do is click the anim button (while the typing caret is still there), it has gone back to 0 before the render begins:



Is there some context in which this is normal behaviour?  If so, how can I change it?
Never mind, I forgot to mention I'm using an add-on, and with that disabled, this doesn't happen.  So it must be overriding it.