i have had a feeling its the mod, which is basically clipping one of the leads to the C11 capacitor... because you're right it should not do this and it didn't always do this (before the mod it was fine) its an easy fix for me as i never actually removed the cap, so i can just open it and resolder... though next step is probably in the right direction by giving it true bypass since as far asi know most if not all of the mxr reissues are NOT truebypass.
this is the link to the mod, though i did not do the switchable (mod/unmod) aspect...
http://www.noisefx.com/article/mxr_blue_box_mod