On a client world, placing any Minecraft block causes them to instantly disappear, with the exception feature that allows blocks to be placed midair next to existing blocks still works. This is being played with several other mods, however this issue is not present when Quark is removed from the mod list. The client log is too long to place into a pastebin, but let me know if there are certain parts of the log I should find, or if I should supply the full list of mods being used along side Quark. Thanks.
Edit: It also appears that changes to settings in the quark configuration are not having effect, even after world reload or starting a new world.