Parameter/sensitivity estimations not possible when using masked blocks

I have been trying to perform parameter estimation or sensitivity analysis on some simulink models, but when I try to add variables the tools don't 'see' any. After a lot of playing around, I figured out the issue where masked blocks: Whenever I disable a mask, the variables defined on the background instantly pop up on the available variables for estimation.

These are not variables which are only defined in the mask or a callback, these are defined as variable either in the initialization or as a model variable (as per instructions on the FAQs). The only difference is a mask menu.

Is there a way to work around this?

Thanks!