Welp one of the following is true:

1) I am doing something wrong. Here is my macro to test:
/say Hello
/in 5 /say Hello again

All that happens is I say "Hello" and I never say "Hello again".

2) You are using some addon that allows this and have not told us about it or you were unaware that that addon was allowing you to do this.

3) You are playing some other game than me. I'm playing WoW... what are you playing?

4) Something else.