This issue affects users running BlackBerry OS 5.0+.
In an HMTL message, when scrolling down to the message content and then back to to header information (attachments, recipients, etc.), the HTML container does not relinquish navigation focus. This results in the user being prevented from scrolling back up to focus the cursor on header information and from being able to select an attachment in order to download or open it.
This only applies to non-touchscreen navigation, so users of devices such as Storm/Torch can select header information successfully using touch navigation.
This is an operating system limitation, however, users can work around this issue by pressing "T" on the device keypad to redirect navigation to the top of the screen.