I can confirm within version DEV320m1,WinXP.
Only first line of formula is imported.

Created attachment 65300 [details]
test file. formula =A4+B4 +C4

Calc Rev. 1520602 gives correct answer of 3 (=1+2)
Excel 2007 gives wrong answer of 6 (cell C4 is not part of the formula)

Win 7

to reproduce:
- open a new sheet in MS Excel 
- fill cell A1 with: 1
- fill cell B1 with: 2
- fill cell C1 with: 3
- add formula to D1: =A1+B1 (here use Alt+Enter to add a new line within the cell) +C1
- Excel calculates 6 to cell D1
- save the file, open it with OO Calc
- Calc calculates 3 to cell D1 (because processing only the first line of the multiline formula)

i use Excel 2013 (15.0.4953.1000 MSO 64-bit) and OO 4.1.3, Rev. 1761381 on windows 7.

Checked with new AOO versions.

Unzip the test file and open <folder>/xl/worksheets/sheet1.xml with a text editor.
There one find the code:
--- code xlsx begin ---
<c r="D4"><f>A4+B4
+C4</f><v>6</v></c>
--- code xlsx end ---

Between “B4” and “+C4” there is simply a “newline”. Maybe the parser stops at this newline.

AOO Calc doesn't allow a newline inside a formula. If one enter a newline it will always changed to a space.
--- code ods begin ---
table:formula="of:=[.A4]+[.B4] +[.C4]"
--- code ods end ---