And how does your system do this: "ll of these fields are supposed to update another field in a seperate table." ?
I'd guess that you are using a script trigger. Script triggers cannot be tripped directly when using IWP.
The checkbox field is writing the data to a separate table via foreign key field relationship. When checkboxes in this layout are selected, the field has a relationship that allows it to write the ID number of the record associated with the checkbox to a different table in an edit box.
On the FileMaker client, this edit box is simply added onto with a "return" for every new line item entered in this way. A portal in a third layout reads these numbers then reports the associated record, sorted and filtered.
On the IWP, whenever the checkbox field is updated (and submitted), it overwrites everything in that edit box with the data from the current tab, instead of adding that data to the bottom of the edit box.
I hope that better clarifies our situation.