using image_tag with google charts url

[Jeff Burton]

I have 9 different image_tag() helper functions with google chart urls as source and one of them doesn't work.

for this particular one image_tag tries to add '.png' on to the end of the google charts link.

I get:
DeprecationWarning: You've called image_tag with a source that doesn't include an extension. Soon image_tag will no longer automatically append '.png' to your source. Please call image_path('http://chart.apis.google.com/chart?...=0,600.png') instead.

Now I've just discovered pygooglechart and that looks interesting. But this is driving me nuts in the meantime.

In all cases the google charts html link is built as a string in a little mako function, and that function is used as the source for the image_tag() helper. In one out of 9 cases, it adds '.png' to the end and spits out the warning. I can't see anything different about this particular string. I'm glad to see that '.png' will no longer be added in future versions, but is there some way to make it stop now?

I'm using version 0.9.6.2

Jeff