I've had the same experience - was browsing the different settings options and the application unexpectedly closed. When I restarted the application, its icon was a red vertical bar. I was thinking of purchasing RTM for my HTC Hero, and have now decided against it. I haven't tried uninstalling and reinstalling...

Running RTM 1.1.3 on an HTC Hero running Cupcake (1.5).

I just restarted the phone. Neither the shortcut on my home screen, nor the one in the applications list popup changed -- both are still showing the RTM cow. Which icon are you talking about?

The main RTM icon in the app list does this. Interesting that yours didn't. Also, when I go into Applications in settings and look at it there, it's a red square. So the home screen must squeeze the pixels into a vertical bar. Either way, it ain't no cow. :-)

Unfortunately this is a problem with the HTC Hero (it's not specific to the Remember The Milk app).

There's more information posted on another forum here.

Unfortunately there doesn't appear to be a workaround to resolve this. :( Hopefully HTC will get this fixed soon!

Emily, it's funny you just posted this... I just was reading the Sprint Hero forum and found out that folks are having this issue. Apparently an update from Sprint is in the works, but they haven't released whether it will fix this issue. Also, not only are icons being mangled on reset, but apps are reverting to previous versions.

That'll teach them to to hack 1.5 to work on CDMA instead of going with 1.6! :-)

Sprint just released a Hero update which has solved this issue for me. Go to Settings -> About Phone -> System Updates -> Firmware update.
This will download the update and install it on your phone.
More info: http://phandroid.com/2009/11/18/ota-for-sprint-hero-users/