Given the following Textile code:

|_.Text|
|!width:50%FE-Image.jpg!|

will throw a 500 error in Redmine with an attachment file called @FE-Image.jpg@ after saving.

ActionView::Template::Error
invalid byte sequence in UTF-8

Stacktrace (most recent call first):

  attachment.rb:259:in `downcase'
    |att| att.filename.downcase == filename.downcase
  attachment.rb:259:in `block in latest_attach'
    |att| att.filename.downcase == filename.downcase
  attachment.rb:258:in `each'
    attachments.sort_by(&:created_on).reverse.detect {
  attachment.rb:258:in `detect'
    attachments.sort_by(&:created_on).reverse.detect {
  attachment.rb:258:in `latest_attach'
    attachments.sort_by(&:created_on).reverse.detect {
  application_helper.rb:657:in `block in parse_inline_attachments'
    if found = Attachment.latest_attach(attachments, CGI.unescape(filename))
  application_helper.rb:654:in `gsub!'
    text.gsub!(/src="([^\/"]+\.(bmp|gif|jpg|jpe|jpeg|png))"(\s+alt="([^"]*)")?/i) do |m|
  application_helper.rb:654:in `parse_inline_attachments'
    text.gsub!(/src="([^\/"]+\.(bmp|gif|jpg|jpe|jpeg|png))"(\s+alt="([^"]*)")?/i) do |m|
  application_helper.rb:605:in `block (2 levels) in textilizable'
    send method_name, text, project, obj, attr, only_path, options
  application_helper.rb:604:in `each'
    [:parse_inline_attachments, :parse_wiki_links, :parse_redmine_links].each do |method_name|
  application_helper.rb:604:in `block in textilizable'
    [:parse_inline_attachments, :parse_wiki_links, :parse_redmine_links].each do |method_name|
  application_helper.rb:625:in `parse_non_pre_blocks'
    yield text

Using the correct syntax:

|_.Text|
|!{width:50%}FE-Image.jpg!|

will display the correct image downsized to 50%.
Is there a way to catch such user-generated error?