One date issue and one date suggestion.
Issue: ToDoIst populates incorrect date.
I attempted to add a task. I clicked on the date widget, scrolled to January 2013, and attempted to select "January 31". ToDoIst populated the date "Jan 1 2013" (i.e., it should have populated "Jan 31 2013").
Suggestion: Allow commas.
In troubleshooting the above, I found that ToDoIst does not accept dates in the format of "January 31, 2013." It seems the comma isn't accepted. I'm sure you've considered this, but I'd recommend allowing for this, since it is typical date syntax.
FYI - looks like this error happens for the 31st of each month. I just tried adding tasks for May and July 31 and ToDoIst converted this to the 1st of each month.
Thank you very much for your report, we are working on this issue right now and will fix it as soon as we can.
Yes, this issue indeed only seems to affect the 31st day of a month. For now, as a workaround, simply type the date in manually, for example: 31/1 or 1/31 or Jan 31 or 31 Jan.
Also, please note that whether Todoist will accept MM/DD or DD/MM date depends on the settings on your account. You can go to the Settings in the top-right corner (gear icon) and on the "General Settings" choose the date format of your choice.