I used FPSpreadSheet 1.8.2 - I was using worksheet protection without password and it worked.
This can't be -- I checked the released source files of v1.8.0, 1.8.2, and 1.8.3, and none of the contains the protection routines. You probably somehow must have got the trunk files.
So should I downgrade and wait for next version to implement worksheet protection with password?
Or load the trunk version from CCR again - trunk is the version which is actively developed, it is always the most recent version. You should use SVN to download it.
Or wait some time until I'll have finished my current activity -- I definitely should release v1.10, the v1.8.x series is rather old...
SVN change log
Workbook, worksheet and cell protection (read/write in BIFF2/BIFF5/BIFF8/OOXML/ODS, write in ExcelXML).
The "SVN change log" refers to the current development version, i.e. trunk.