The recent versions of the 1.26.8 viewer for Windows doesn't reflect the changes of the light sources made by the lsl scripts. In other words, one cannot switch on/off any light bulb. How to reproduce: create a prim, put the trivial light bulb script in it (like this one):
Then click the prim. Nothing happens. In the Edit window, the Features->Light checkbox is changed in the right way, but there is no light (or no darkness, if you have started from the "light on" state). Releases 1.26.8(11) and 1.26.8(12) for windows are affected, release 1.26.8(9) is unaffected (I have re-installed it from backup to test this).
P.S. Looks like another "broken light bulb" joke, but this is for real. ;-(
Update: 1.26.8 (13) is still affected. The last version without this problem seems to be 1.26.8 (9).