The Palm Device has a maximum length of 4,096 bytes (4k) on memopad entries, if you wish to retain the ability to edit the Memo (add/remove/change data within the memo) on the Palm itself. You can create a memo entry of 65,490 bytes in size (the absolute maximum) if you do not need to edit the memo entry any further on the Palm device itself. Any memo larger than 4,096 bytes and less than 65,490 bytes will not be editable on the Palm itself. Consider these memo entries "read-only".
This is not specifically a "bug", but a limitation in the PalmOS design itself.