Exactly, thanks a lot for posting, that was the one.
I was totally going to post this.... before you posted it!
Kaidan is in fact my fav example of how presumeably straight companions can turn out to be bisexual later in the game and still make sense. <3
There were indications that Kaidan was supposed to be romanceable by both male and female Shepards in Mass Effect 1 but was scrapped before launch. Dialogue was recorded by Mark Meer (the VA for male Shepard) which clearly showed romance with Kaidan was possible. A modded game can open up the dialog but it is not 100% perfect; characters will call your male Shepard "Ma'am", refer to him as 'her' and in the love scene towards the end, your maleShep turns female for a few seconds. However, when a modded ME1 file save is imported to ME2 or ME3, the game registers the same-gender romance with no further glitches.
I was hoping that when the Mass Effect trilogy was announced that Kaidan might finally be available to maleSheps for ME1 but alas, it was not so.