In its current form, if a user is inserting a fitting in non-spec-driven piping, a window appears to allow the user to select their desired entry-ports and orientation points. However, this window does not show any of the datums if the model is saved with its layers turned off. Therefore, if the layers are hidden for that model, there is no way for a user to select those coordinate systems or points. Even a CTRL+F does not show results on a first try (a hidden work-around is to force it to find the coordinate systems by manually changing the "look-in", and simply re-selecting the model in the pop-up window.
Please change this window to include a model tree and layer tree. This would probably be the easiest way to solve the hidden-layer issue.