澄んだ水面 が 月を映していた。
Under the 映す entry in a dictionary (ルミナス、研究社), I found the sample sentence in question among others. However, I couldn't understand why only in this particular sentence is が used in favor of に.
For instance, there were also these two sentences listed right beside the one above:
彼女は鏡 に 顔を映してみた。
彼はスクリーン に スライドを次々に映した。
Both of which employed に as I normally would expect.
The only plausible reason I can think of is that the first sentence does not have an animate subject (月), whereas the others do (彼女、彼). I do not believe this is the factor though.
Interestingly, for the verb 映す's intransitive counterpart－映る－they gave the following sample sentence:
月が湖水 に 映っていた。
Can が be replaced by に in the first sentence (i.e. 水面に)? If not, what is the grammar at work that prevents us to do so?