Why does the presence of a non-numeric range value shift labeling of a DateListPlot?

Question

Consider the following code:

DateListPlot[{{1514820721, 3}, {1514969636, 5}, {1514969637, Mean[{}]},
              {1514969952, 5}, {1514993369, 4}}, DateFunction -> FromUnixTime]

I spent quite some time looking why the dates appear shifted (the list here is a simplification of a much larger data set) only to find that if I remove the entry with non-numeric entry of Mean[{}], then the dates are as they should:

DateListPlot[{{1514820721, 3}, {1514969636, 5}, {1514969952, 5},
              {1514993369, 4}}, DateFunction -> FromUnixTime]

Now I wonder: what's happening here? Why does the presence of this non-numeric entry in the input list result in shifted dates on the X-axis?

Answer 1

Looks like a bug to me, because you would get the correct labeling if you were to make the time conversion on the data before you passed it into DateListPlot

data = 
  {{1514820721, 3}, {1514969636, 5}, {1514969637, Mean[{}]}, 
   {1514969952, 5}, {1514993369, 4}};
data1 = MapThread[{FromUnixTime[#1], #2} &, Transpose @ data]
DateListPlot[data1]

Update

I reported this to Wolfram tech support and received the following reply (edited to omit boilerplate and other non-relevant material).

I was able to reproduce the issue, and consequently, I filed a report with our development team raising the issue ....

Therefore, I am tagging the guestion with bugs