I happened to come across this post a year later lol and I think I can explain why this is so. You get the fury buff from Icarus when you parry, then buffet consumes it hence it is expired and as a result you get the degen. The same interaction happens with DS on the same quest as his counterspell reliably nullifies the furies you get from Icarus and you practically constantly have degen on you unless you have Ghost. Nullification of a buff is considered as expiration so I guess this is working as intended.