Yes. There is a 255 character limit set in AXF files. When editing a field with more than 254 characters, the edit cannot be checked back into the SDE database. This is a known issue because of the 255 field character limit set in the AXF file, which is a Microsoft SQL Server Compact Edition relational database.
As a workaround, add a new 254 character field or less, and update the custom form accordingly to allow for additional notes.