I’m pretty sure this is not default behaviour as when using a time axis scale with a bar chart, the bars overlap. If you compare this to a standard bar chart the bars would shrink in size. The screen shots are taken from the samples.
As far as I can work out I believe it could be to do with the calculation of the width based on the number of ticks. As the ticks are reduced on the time version to fit the label in the calculation should really still use the number of points. But so far I have not manage to find the exact location in the source.