Since I upgraded to version 1.5 there's a gap between the perimeter and infill.
This is due to a fix to the way infill overlap is calculated. 1.4 and previous versions took the value entered and added half the nozzle diameter, making the actual overlap much more than was actually specified in the Infill Overlap setting. Thinking this was untrue to what the field is supposed to be, the development team changed the behavior to more accurately represent the value entered.
So, the solution is to add half the nozzle diameter to the Infill Overlap value. Infill generation should then work correctly, and will be back to the way it was before the update.