I found that this affects most instant-cast abilities because they aren't really "instant" per-say due to latency between server and client. Summoners may have noticed this when using Bane immediately after casting one of their DoTs (Bane doesn't spread the last DoT). What is happening is that after you use an ability, the client has to let the server know that you cast said ability, and then the server has to acknowledge it and apply buff/debuff and assign the proper status icon. If you use Swiftcast, you have to give it 300-500ms minimum to allow for the server to realize you used that ability and adjust if you're experiencing higher latency. You'll know when Swiftcast is ready by looking for the icon to appear in your buff bar. If you Swiftcast and Raise too fast, you'll actually start casting Raise before Swiftcast is acknowledged and Raise will cast normally, which means the Swiftcast buff will apply to the next skill instead.