OK. I have just installed the latest devel version, 8.7.9, and it works. So I guess it was a bug in 8.6.x that is now fixed in devel version. Right?
I don't recall a bugfix for this specific problem, but looking for the fix, I found a ticket --
https://htcondor-wiki.cs.wisc.edu/index.cgi/tktview?tn=6219-- which made me wonder if you switched the '+special2' to 'MY.special2' if things would work for you in 8.6.
- ToddM