User macro param doesn't work as expected for iframe

Summary of the bug

Create iframe using user macro with 3 params. $param0 indicates the src, $param1 indicates width and $param2 indicates the height. In the page where you use the macro, if the $param0 ( src ) contains parameters (particularly equals-to sign), the page cannot be displayed and throws Page Not Found in Confluence.

How to reproduce

Create a user macro with these parameters:
Macro Name: myiframe
Macro has a body : Untick / Tick (Both)
Output: Macro generates HTML markup

Template:
<iframe src="$param0" width="$param1" height="$param2"></iframe>

In the page:

This will result in Page not Found (within Confluence). Click the link for the image.

Extra Findings

• When the URL is hardcoded in user macro, the external page is displayed correctly. Eg:

User Macro

<iframe src="http://spreadsheets.google.com/pub?key=pwS2wRVw9u1dK1ujYw5AaAA" width="$param0" height="$param1"></iframe>

Page

• The problem happens during the passing of parameters. Could be due to double equals-to sign. Eg: src="http://spreadsheets.google.com/pub?key=pwS2wRVw9u1dK1ujYw5AaAA"

• Page source indicates the $param0 is not expanded: <iframe src=$param0 width="800" height="400"></iframe>

• There is no problem if the user macro is tried within the {html} macro. Eg:
  {html}

  <iframe src="http://spreadsheets.google.com/pub?key=pwS2wRVw9u1dK1ujYw5AaAA" width="800" height="600"></iframe>

  {html}

Workaround

Escape the equals to sign (=) with &#61; Eg:

{myiframe:http://spreadsheets.google.com/pub?key=pwS2wRVw9u1dK1ujYw5AaAA|800|400} 

The result is the expected result as indicated in this image