text: Title: problem, random cells write as zero
  Body: Hi hi :3
  
  I found this writing data with pandas + xlsxwriter, actually some formulas just don't are written correctly, and are not exactly random, lets test with this code:
  
  ```
  import pandas
  
  a=[]
  
  for i in range(50):
      a.append("=1+1.0")
  
  dd = pandas.DataFrame(a, columns=["test"])
  
  dd.to_excel("test.xlsx", engine='xlsxwriter')
  ```
  
  In the result xlsx we should have 50 equal formulas, but, in the cell B4 I get 0, and is not like the value has not been evaluated, literally the formula of the cell is zero, I don't know why that formula is not written...
  
  Is "random" because from all that "equals" formulas some of them just don't works, but is not random because the cell with the problem is the same in some iterations, after some of them it change.
  
  (every iterations is running the same code again)
  
  A clue, if we use "=1+10" without decimals works, at least with 50 results.
  
  If we want to get a similar result getting zero every where, use "=1+1,0".
  
  The first time I run the script, the formula we read in the file is "=1+1.0", as we wrote, testing again and again I get "=1+1" for some reason... now we don't have the ".0"...
  
  I'm using WPS, but all what I wrote here I check it with the formula bar, not the results.
  
  Thx.