Hi Jarred,
using a CheckBoxSelectionModel inside Grid automatically adds needed column config as first column, that includes this.selModel (CheckBox column).

After promoting a column too a class and using it as a link, the checkbox column is lost (will not be generated as first column). The funny thing is, that this bug only occurs if promoted class is the first column.

In this case i created a mimetype column that should be used on different grids.

As a workaround, you can use
this.colModel.config.unshift(this.selModel);
right after calling superclass.

Greets Holger