The problem is that some forums have the "Post Icons" feature enabled and others do not. Ideally they should all have it disabled since AAM is configured such that posters cannot choose special icons for new threads in any case so for forums with Post Icons enabled the default icon above will be used automatically. The feature is sort of pointless generally and certainly so in the existing AAM configuration where users cannot choose a thread icon. I or somebody else will go through the individual forum settings to ensure that Post Icons are disabled for all of them.