If content is copied and pasted from another source (i.e. Microsoft Word), formatting from the source HTML can be accidentally added into the custom form.  

Best practice is to always choose "Paste as plain text" when adding any content from another program.  To ensure you are pasting as plain text:

From a PC:

  1. Highlight and copy the text.
  2. Click the right mouse button to insert text into the form.
  3. Choose "Paste as Plain Text".

OR

  1. Copy and past text into notepad (or similar program) first.
  2. Then, copy the text again and paste it as Plain Text into the Custom Form.

From a Mac:

  1. Highlight and copy the text.
  2. Paste into your Mac Notes (Text/Edit).
  3. Copy that text and paste it into the Custom Form.

OR

  1. Copy the text.
  2. Right Click to Paste and match style.

OR

Click the Command+Shift+V buttons simultaneously.