You created an extension field of type Text and have defined a limit of characters for this field, when using this field in UI, you are receiving a max limit message even you entered an amount of characters less than the max limit.
SAP Business ByDesign.
This is the expected system behavior. The counter also consider the line breaks and spaces as characters.
In this case you can remove unnecessary characters or create a field with a bigger length.
Text Field, Characters , KBA , AP-RC-UIF , C4C UI Framework , Problem