Your first macro is how you would expect it to work. Your second macro works due to the same issue that normally makes you lose dps when you use a castsequence. The castsequence waits with casting the next spell until your client thinks it has finished casting the previous spell. While the castsequence is waiting for the previous spell cast to finish, it doesn't trigger the global cooldown and the macro falls through to the next command. Due to lag the server normally finishes casting the previous spell a 100-200ms earlier then the client expects it to be cast. This creates a small time frame during which the fall through spell can be cast.

Note that this fall through casting trick depends on both your lag, haste rating and the cast time of the spells used. Spells that have a casting time that matches or is close to the global cooldown, can prevent this trick from working.