EDIT Posts overlapped. Refers to @eschwartz and @BetterRed
Generally you have're right to be angry.
Now I have changed the code from previously [strike][/strike] to [strike]_selection_[/strike] - and it works as expected.
Admittedly I had overlooked this
available variables affair.
But I also assumed the habit in dealing with these tags that the default setting is to surround marked text if such exists. This is in MR and other forums I know the case.
I suspect that you are no longer interested in the following, but I mention it. The unfinished/unbalanced in Firefox which can always give rise to further conclusions (of production depth) we see (here) in the name of entry field:
Don't these devs see that!?