Forestry wooden log blocks have 4 subBlocks and also rotate, all based on meta.
When buildcraft registers facades, it will only get the first wooden log subBlock and skips the other 3 because it's also a rotatable block. This means that 3/4 of Forestry wooden logs don't have facades.

I wanted to just make a PR but I couldn't quickly think of a clean way to do it.
Personally I would like to register all sides as facades and remove the duplicates (for creative mode). There may be good reasons not to do so however.

The relevent Buildcraft code is in ItemFacade registerValidFacades.

I'll be happy to submit a PR once I know what direction to take this.

Trying to extend default facade support has caused many many problems in the past, I think we want to get back to something minimal, with mod-specific possibility of extension. Such extensions will be considered as part of the forthcoming https://github.com/BuildCraft/BuildcraftCompat project, I suggest to work on this there.

That makes a lot of sense, thanks.