com.atlassian.confluence.servlet.simpledisplay.ConvertedPath.getPath() uses Velocity.evaluate() which uses a singleton VelocityEngine that is internal to Velocity code and I think it hasn't been initialized from Atlassians velocity.properties file.

So it's using default settings and trying to write a velocity.log file.

All the other Confluence code I've seen gets an engine from VelocityManager.