The program was no longer converting the input joist spacing in even hundreds of mm, e.g. 400, to a spacing in even inches, e.g. 16, when changing from metric to imperial, and vice versa. The default spacing of 400 mm therefore changed to 15.8" after changing the setting to Imperial. A default 16" spacing converts to 406mm.
Previous to version 8, the program would convert 400 mm to 16” and similarly for 300 and 600 mm (12 and 24"). This behaviour has been restored.