interesting issue. If you add a small number to LOAD_DURATION like
or use the small number without LOAD_DURATION, the fraction will appear, but only showing the addtional number (I tested this with an variable and text box output, I think LOG is a function defined in your script, right?).
I thought of truncation of LOAD_DURATION during interval evaluation, but my modification shouldn't work then neither.
Also printing LOAD_DURATION and sum of LOG_DURATION+1e-006 looks fine.
So I can't see a problem with the format and use of interval function, I am also clueless. This absolutely does not look logically to me.