The backslash deleted

Hello
I just installed the current version of anspress.
I have a problem: the backslash \ used in latex code  are delted in the comments (something that doesn’t happen in the questions). This is an example:
If I send :

\frac{x}{y} + \sum_{k=1}^n a_k

it becomes:

frac{x}{y} + sum_{k=1}^n a_k

that is to say without the backslashes.
Thank you for helping me overcome this problem.