Running Filemaker Pro Advanced 188.8.131.520 on OSX 10.13.2 using a bluetooth apple mouse (Magic Mouse 2) on a MacBook Pro.
This is really minor and seems to be somewhat machine configuration specific but it's bit me several times in the last few days and seems to be new behavior. Basically, if you have defined a field with "select entire contents on entry" and you click once on the field with the mouse it does the right thing. If you click again, an insertion point shows up while the mouse is down but the entire field remains selected and the insertion point goes away upon release. Eventually, if you click enough times you can get an insertion point. If you use the keyboard arrow keys you can always get an insertion point. If you use the trackpad it always behaves correctly so this might be a mouse on a machine with a trackpad issue. Once you get an insertion point it seems to work correctly for all fields in the layout until you load another record when it goes back to the incorrect behavior.