Cannot insert sheet in .ods file

[Dond3320]

I have a LibreCalc file created from scratch. It consists of 7 sheets which I had no problem creating using the "right click" with the cursor over the green plus sign at the end of the sheet list and selecting the "Insert Sheet" option on the pop up menu.

Don't know exactly at what point this function was lost but, for this Calc file only, so far, the menu that pops up using "right click" as above no longer contains the insert sheet function; it is not greyed out; it just isn't there. In the menu for the "Insert" function the "Sheet" option is greyed out. The file is not protected. What could I have done with this file to create this problem and how do I fix it??

[TheGurkha]

It's a left-click on the green + that creates a new sheet, not a right-click. If I right-click the grey area to the right of the green + I get a context menu with the insert sheet option in it.

If you start a new spreadsheet altogether can you use the green + to add a sheet?

[Dond3320]

On my system it's a right click and to answer your question, on a new spread sheet or on all others, new or old, I've worked with since switching to Ubuntu, a right click gets me the option to create a new sheet and exercising the option creates a new sheet. I remain baffled.

[RoryOF]

Trying AOO 3.4.1 on Ubuntu 12.04 a left click on the blank space after the sheet tabs immediately pops up an Insert Sheet window, a right click pops up a context menu, offering Insert/Delete/Rename and other sheet functions, as well as Cut/Copy/Paste.

Edit: there may be a difference here between AOo and LibO, as I cannot see any green + sign.