In a Rich Text field:
On a normal paragraph line that begins with a linked entity, moving the cursor to the beginning of the line causes the cursor to disappear.
The cursor is still actually there, and it will become visible when it’s moved, or a character is entered.
ALSO: when the cursor is at the beginning of the preceding or following line, and is moved up/down to a line that begins with an entity reference, the cursor moves to the end of the line (following the entity reference) instead of the beginning of the line.