I've created a custom write() method for the crm_lead model. Its purpose is to do some checkups when the stage of a lead/opportunity is changed and raise an exception if necessary.

This works fine if the stage is changed via the form view (by clicking the stage widget at the top), but if the change is done via the kanban view by dragging and dropping, it does not. The exception does still get triggered, but the message defined in raise osv.except_osv() does not get shown to the user, instead an alert box with the following message is shown:

An error has occured while moving the record to this group: undefined

Can I show a customized error message to the user in Kanban view? Since this popular question does not have any answers yet I'm not sure if this is possible to achieve.