Hi psandr, this appears to be a bug with math containers that affects Maple 2017.3 as tomleslie states. Please note that this issue is fixed in Maple 2018 to be released later this year. 

If you are planning to use this grading code in Maple T.A. or Mobius, please also note that because the issue is with math containers and not the grading code itself, it should work properly in both of these environments.

I haven't heard of this being done, but it might be possible to add the toolbox to TA. If it is possible, it would need to be set up by the system administrator or Maplesoft (if it's hosted with Maplesoft). There are no guarantees that such a setting would work in the TA environment however.

What question type are you using? Formula Without Simplification can be used with the Mathematical Formula type, but this type of question does not accept $variables in the answer part I think.  At least I am getting an error when I try to submit the response area with a variable in it.

You may have to move to Maple-graded to do this, but you will have to specify in the code that you do not want simplification.  If you can include a copy of your algorithm and screenshot of the question, I can take a look.