I'm sorry for the longwinded response. I wouldn't blame you if you don't read it...
I've attached a screenshot which will help with understanding what I'm dealing with.
There's a main form (configured as a split form) with three SubForms at the bottom of the screen. The record displayed on the main form is called MileStone_Dates and has a PK called DB_Key. All of the SubForms have a FK called Milestone_Dates_DB_Key. The Subforms are linked to the Main Form as you would expect (Milestone_Dates_DB_Key = DB_Key).
The SubForm who's Current event is being triggered is the Information Requests SubForm. Interestingly, the Current event for the other two forms is not triggered in the same way.
The ComboBoxes framed in red are required values (defined as not null in the database).
The ComboBoxes which are the "problem children" (triggering the Current event of the Information Requests form) are; Regulatory Sector, Directorate, Team, and Type.
These ComboBoxes all have a MouseMove event which calls a Subroutine which dynamically builds their RowSource (I set/check a variable to ensure that even though there are multiple MouseMove events the RowSource is only built once).
What's odd is that Project Name, Group, Category, Purpose, and Application Decision are all similarly configured to the "problem children" but do not trigger the Current event of the Information Request SubForm
What you can't see is that for each of these combo boxes there is a TextBox placed over the Combobox which displays the current value of the column (the underlying query joins all of the reference tables to get the current value). The text boxes do not have a tabstop. Tabbing from field to field navigates from one ComboBox to the next There is an click on the TextBoxes event which sets the focus to the corresponding ComboBox. The GotFocus event of the ComboBox calls the same SubRoutine as the MouseMove event.
Further testing has revealed that the same behavior occurs with the GotFocus event. This tells me that the problem is not related to the mouse move event at all. I checked to see if the main form's Current event was being trigged some how (and subsequently triggering the Current event of the SubForm). This is not the case.
Please let me know if any of this twigs anything for you.
Thanks again for spending some time to think about this.