Note that ‘verbless grammar’ (i.e. 'Understand ... phrases that start with a [token in square brackets] rather than a verb word) is still not fully supported in Inform 10.1.2.
The bug in 9.3/6M62 that led to incorrect allocation of topic snippets after commands such as ‘Darcy, hello’ (see here) when a story included any verbless grammar has been fixed in 10.1.2, but it remains the case that if you have a word that is both a true recognised verb word and also a word that is recognised by your ‘verbless grammar’ token, the parser will try to parse it only as a true verb word and never as a match to the ‘verbless grammar’ token (see also here).
In this instance, if you name your spell as a word that is already a true recognised verb word, your spell will never fire because the parser gives up after having failed to match a correct grammar line to the recognised verb word without then going on to consider the possibility of matching to ‘verbless grammar’.
e.g.
Lab
>name spell answer
You name your spell Answer.
>answer
I didn't understand that sentence.