It fails to export a date type because the cell value is interpreted as a double type.
Created attachment 31148 [details] [PATCH] patch
Thanks for the patch, committed in r1564011. This will not make it into 3.10 any more, but be included in the next release.
Created attachment 31821 [details] Exports formulas correctly to a xml document
The patch I provied on december 23 does not take into account formulas which return dates. E.g. POI does not handle excel cells correctly containing formulas like: =Date(2013;12;31) The POI XML exports results into a numeric value instead of a date string. I wrote a patch for the current trunk code which handles that correctly.
Reopenend because POI fails to export cells containing formulas which return a date value.
Thanks for this, applied (with minor tweaks) in r1614696.