In version 3.5 the protection changed. Commenting the old $buf does not work anymore.

Find

\components\com_sef\joomsef.php

you will see like this :  $cacheBuf2 =

        'PGRpdj48YSBocmVmPSJodHRwOi8vd3'.

        'd3LmFydGlvLm5ldCIgc3R5bGU9ImZv'.

        'bnQtc2l6ZTogOHB4OyB2aXNpYmlsaX'.

        'R5OiB2aXNpYmxlOyBkaXNwbGF5OiBp'.

        'bmxpbmU7IiB0aXRsZT0iV2ViIGRldm'.^M
        'Vsb3BtZW50LCBKb29tbGEsIENNUywg'.^M
        'Q1JNLCBPbmxpbmUgc2hvcCBzb2Z0d2'.^M
        'FyZSwgZGF0YWJhc2VzIj5Kb29tbGEg'.^M
        'U0VGIFVSTHMgYnkgQXJ0aW88L2E+PC'.^M
        '9kaXY+';

Comment this block.