Seems like scanning all blocks including from mods is too ambitious for facades, see reports like http://mod-buildcraft.com/forums/index.php?topic=17.0 or http://mod-buildcraft.com/forums/index.php?topic=16.0. Revert to the initial behavior only considering standard blocks. Alternatively, an exception handler might add the necessary level of safety around the code, and allow much more facades.

Yes, I originally stopped doing this a while ago, because mod blocks are fiddly to get right. Let the mods tell you which ones to facade using IMC..

Since we're still in beta, I'm going to leave for a try with the exception handler. See what the feedback is. Problems will show soon enough if it's still not appropriate.