That's actually one of the big discussions we get into...can one change their orientation because of HRT/transitioning?
Some do (possibly because they were suppressing their "true" orientation (gay or straight)), or perhaps their orientation (i.e., their preference) stays the same, which makes it look like their orientation changed...and finally maybe orientation isn't as carved in stone as we might think it is. We know that gender tends to be more fluid (some like water, some like molasses...either way, still fluid)...so I suppose it's possible for sexual preference to be more fluid as well.
No matter what...just go with it, if you're comfortable. If not, explore yourself to find out why you're not. (There are legitimate reasons for both).