This issue has been observed on NotifyLink Blackberry devices running OS 5.0 when composing a reply. If you leave the composition area to scroll through and reference the original message, the device will not allow you to resume typing the reply. You are able to continue to scroll up and down to see what was previously typed, but you cannot continue to type.
There is currently a BlackBerry limitation when using the 5.0 OS, that will not allow the client to regain focus on the reply portion of a message when responding to an HTML email.
A work around for this BlackBerry limitation is to save the message as a draft on the device. Then navigate into the drafts folder and re-opened the message to finish composing the reply.
With NotifyLink v4.7.4 and NotifySync v4.8.4, you may also use the Resume Compose menu option to regain focus in the composition area.