To reproduce:

• activate debugstirngids in Site administration->Development->Debugging
• save reload and/or navigate to other page
• no string origin is displayed
• go back to Site administration->Development->Debugging
• turn on Debugging and set "debugdisplay" to yes
• save and reload and/or navigate to other page
• no strings origin is displayed

Maybe the function has been removed, in this case it may be worth removing it form Debugging settings. Under certain circumstances, the debugstirngids function is very useful to a Translator's work.