Part of it is he is waiting too long. What is he doing at the time - my son was playing on the computer. He's acting out, but I would not overly discipline him as there is something underlying that is causing it - something small that could be stressing or upsetting him. This is his only way to 'get it out' so to speak.
My son did this last year after he started school. The cause was a change in teachers (we ended up having three different ones, if this gives you an idea of the instability they went thru.)
I am positive your husband's absence is a big part of this - if this is new for him or it has been more frequent. Also, look at school or any other small thing in the home. Parents do not realize that the smallest event can upset a child. In example.. My SIL redid her kitchen over...she repainted the whole kitchen and retiled the floor and had installed new window treatments. Doesn't seem like much when you think on it, but that made my nephew revert to accidents due to the stress over the change.
In many posts like this over behavior, I try to stress that it doesn't take much to upset the loves of our life. :)
For us, we remained constant and as he reverted back - we reverted back to the ways of potty training. I also sent him to the potty every hour - just as I did in potty training. Patience, understanding there is something there (and talking to your son - they will respond - even if you use a puppet as we do.), and knowing it will pass.
But I would say it is indeed a stage.