only last /spend in issue comment taken into account

Summary

if I add this comment to an issue :

/spend 8h 2019-07-02
/spend 4h30m 2019-07-05

the preview shows :

Adds 1d spent time. Adds 4h 30m spent time.

but when I submit the comment it only adds 4h30m and shows:

@Mathieu added 4h 30m of time spent at 2019-07-05 just now