Find In Path - inconsistent result

Inconsistent result for 'Find in Path' between (1) paste (2) typing from scratch (3) delete last character

1. Open file in source folder (not excluded) and copy some text - abcde.

2. Go to source folder for the file, 'Find in Path', paste abcde. Result: Nothing to show

3. Delete abcde, start typing:

           - a - results are found, ab - found, abc - found, abcd - found, abcde - found

           - delete last character e, so it is now abcd - Nothing to show

'Invalidate Cashes / Restart' does not help

IntelliJ IDEA 2017.3.4 (Ultimate Edition)

Build #IU-173.4548.28, built on January 29, 2018