I'm having a problem with specifying a default for a parameter in a template.

If I give the parameter in the template as: {{{Param|None}}}
When the value is unspecified in a page I get: {{{Param|None}}} (printed plaintext)
When the value IS specified in a page I get: {{{Param|None}}} (printed plaintext)

If I give the parameter in the template as: {{{Param}}}
When the value is unspecified in a page I get: {{{Param}}} (printed plaintext)
When the value IS specified in a page I get: (the value printed plaintext)

Basically it doesn't seem to recognize the parameter-with-default as being a parameter at all, it just prints it out plaintext regardless of whether it is specified or not. If I don't give a default, then without a value it prints the plaintext parameter, and with a value it prints the parameter properly.

Does this make any sense? What might I be doing wrong? I have read the appropriate meta help carefully and as far as I can tell I'm specifying my default properly.

Thanks in advance for the help!