Graph of a function has breaks when the value equals the upper limit of the Y
axis, "XY Chart" graph type.  

Observed in OOo2.2, Windows.  Not in OOo2.1 and earlier, Windows and Linux. 
Suspected regression.

I exported as PDF, and the gap is in the resulting PDF file.  Therefore, I chose
"formatting" instead of "viewing" or "printing".

Procedure:

1) Create new spreadsheet.  File|New|Spreadsheet.
2) Create series in A column from 0 in A2 to 100 in A102.  I set A2 to 0, A3
"=A2+1", and then copy and paste through A102.  Also set A1 to "x".
3) Create function in column B.  Set B1 to "sin(x)".  Set B2 to
"=sin(radians(A2))", and copy and paste through B102.
4) Select the A and B columns.
5) Create XY graph.
  a)  Insert|Chart.
  b)  Next.
  c)  Click "YX Chart" icon.
  d)  Next. 
  e)  Click "Lines Only"
  f)  Create.
6) Observe the gap at x=90.
7) Enhance the view (optional).
  a) Double-click the chart.
  b) Double click the function graph, "Data Series 'sin(x)'".
  c) Select the "Line" tab.
  d) Increase the width.  Click its up button a few times.  For en-US, 0.10" is
good.
  e) OK.
  f) Gap at 90 is now more visible.
8) Slightly increase the upper limit of Y, and gap disappears.
  a) Double-click the chart.
  b) Double click the Y axis.
  c) Select the "Scale" tab.
  d) Set upper limit to 1.1.  Turn off Automatic: Alt+T.  Set value: Alt+X, then
1.1.
  e) OK.
  f) Gap at 90 is gone.