Quote Originally Posted by Antonio1986 View Post
For example ванная remains female because the подразумеваемое слово is комната.
That's exactly the point, in that case ванная can only refer to one specific thing, which is комната. When you say единственное, что... единственное can refer to a multitute of things there, there is nothing specific that immediately associates with it, that's why it just must be neutral. Almost the same as вещь btw, you don't really know what the nature of вещь is until it's clarified further along in the sentence, but as вещь is a proper noun with its own gender, grammar rules demand you use femenine with it.

Congrats on becoming завсегдатай, let's hope I'll reach that high one day as well