If you name a plugin with capitalization in it (in the atlassian-plugin.xml), then the macro will never be found.

On the other hand, as long as it's lower case, any capitalization for calling it works:

{myPlugin}

,

{myplugin}

, etc.

I suspect, toLowerCase got called in one direction, but not the other.

This should at the very least be documented in bright red letters on the How To Create Plugins documentation.