Created attachment 29948 [details] Test program exhibiting the bug DateUtil.isCellFormatted(Cell) returns true for a numeric cell that's formatted as ".0000". Tracing through the code, this is because DateUtil.isADateFormat(165, ".0000") is returning true. That's obviously not a date format; maybe date_ptrn3 needs to be made more strict? I've enclosed a simple program which exhibits this.
Thanks for the report, fixed in r1445725.