After a few more testing, I began to get a hint on how it happened: under normal usage of the Form Module, you are right, it works as expected, the issue can't be replicated. Here is the my usage of the Form Module: I used it to update joomla users table for logged-in user, so each logged-in user can ONLY update his/her own account information using Fabrik Form Module(by setting Row id(-1)/use key(id)/Ajaxify(No)), he or she doesn't has Add records Access permission on the users list(only given Edit records or use field(id) under Lists -> Access tab of the users list), also enable Ajax validation under Forms -> users(Form processing tab)/ Toggle Submit(No). So the issue can be duplicated when you tried to add any extra field to the users list and attach a validation rule to it, you can try to violate the validation rule(for example: be empty on NotEmpty rule) on the field when update(edit) your user information using Form Module and submit it(fyi: I just want to use the Form Module for each logged-in user to update his/her user information, I don't want logged-in user to add any new records on the list, I don't know how to achieve this). After submitted, the Form Module for the users form simply just disappear which I believe somehow after validation failure and submission the Form Module rendered(switched) itself into the "Add New Record" mode from the previous "Edit mode"(by totally ignoring the setting of Row id(-1)!!??), because the logged-in user doesn't have Add Records permission which can explain why the Form Module's disappearance from the interface after the validation(also the disappearance will sustain even after refresh the webpage, the form will only shown up again after logged-out and logged back in again, it seemed got stuck on the Add New record mode after validation error/submission if logged in as non-Super Users). Can this be treated as bug? -- for its behaviours(Edit vs Add) are different (Before vs After) validation failure/submission. Hope I make my case clear and understandable. Thanks, -Rick