Hey, My Shepard loves Miranda (mainly the arse, but he also likes her a person xD) and Miranda felt the same way. (She loves Shepards arse too, alotta arse loving) So when I activated the suicide mission Shepard and Miranda made sweet sweet love, and all was well and good. After the not-so suicide mission (everyone lived) I go over to speak to Miranda, but when I ask her to 'chat' so speaks the same dialogue she said before we did the 'deed'. She says she'll meet me when it's quiet, totally oblivious to the fact we've already made love. It's like we never made love in the first place.  
 
Has anyone else experienced this? Is it some sort of bug in the game or is it supposed to happen? Also does anyone know how I re-activate the 'love scene' between them after I've beaten the Suicide mission? I want to have some sort of relationship going into ME3 and don't want to be locked out of one because of a weird glitch if it is one.

If I remember correctly everyone does that after the suicide mission because the game is over. If you want to know if your romance still works, you can go to the captains quarters and call her up to your room. The love scenes, as far as I know, are not repeatable.

I called my last relationship a glitch as well.
 
And it sounds like your Miranda is trying to re-live the moment but not really succeeding. Unless it works every time?

Maybe you just weren't very good.  Call it a 'glitch' if it makes you feel better.

From what I can remember Youcan still call off the relationship and be able to pursue another after the game ends