did you try this fix?
FIND IN
gtpm_quickreply
HTML Code:
<div align="$stylevar[left]" style="max-width:$stylevar[messagewidth_usercp]; width:auto !important; width:$stylevar[formwidth_usercp]">
REPLACE WITH
HTML Code:
<div align="$stylevar[left]" style="max-width:$stylevar[formwidth_usercp]; width:auto !important; width:$stylevar[messagewidth_usercp]">
if yes, what are your values for the following settings?
Stylevar / User Control Panel Form Width (pixels)
Stylevar / User Control Panel Message Area Width (pixels)