In Parshas Bo ([Exodus 12:8][1]) it says about the [Korban Pesach][2]:

>וְאָכְלוּ אֶת-הַבָּשָׂר, בַּלַּיְלָה הַזֶּה:  **צְלִי-אֵשׁ וּמַצּוֹת, עַל-מְרֹרִים יֹאכְלֻהוּ**.
>
> And they shall eat the flesh in that night, **roast with fire, and unleavened bread; with bitter herbs they shall eat it.**

but in the Parsha of [Pesach Sheni][3] in Behaalosecha ([Numbers 9:11][4]) it says:

>בַּחֹדֶשׁ הַשֵּׁנִי בְּאַרְבָּעָה עָשָׂר יוֹם, בֵּין הָעַרְבַּיִם--יַעֲשׂוּ אֹתוֹ:  **עַל-מַצּוֹת וּמְרֹרִים, יֹאכְלֻהוּ**
>
> in the second month on the fourteenth day at dusk they shall keep it; **they shall eat it with unleavened bread and bitter herbs;** 

Why are these two commandments phrased similarly but differently, with the first one apparently indicating a tighter coupling between the korban meat and the matza?

  [1]: http://www.mechon-mamre.org/p/pt/pt0212.htm#8
  [2]: http://en.wikipedia.org/wiki/Korban_Pesach
  [3]: http://en.wikipedia.org/wiki/Pesach_Sheini
  [4]: http://www.mechon-mamre.org/p/pt/pt0409.htm#11