ID 362908 - Enabling the read file, "reading" knob on a Write node changes the file_type knob

Problem summary
Enabling the read file, "reading" knob on a Write node changes the file_type knob.

This appears to happen for all file types expect .null, however the files are read in correctly

Customer reported version
nuke.11.2v2

Customer reported platform
windows10

Steps to reproduce

1) Open Nuke 11.2

2) Create a CheckerBoard and connect a Write node

3) Set the file path to test.exr

4) Enable the read file knob, the file_type will change to something other than exr

Reproduced by support
This bug has been reproduced in:

Nuke 11.2v3 - Windows 10 - CentOS 6.9 - MacOSX 10.13

Nuke 11.2v1 - Windows 10 - CentOS 6.9 - MacOSX 10.13 - regression

Unable to reproduce bug in:
Nuke 11.1v5 - Windows 10 - CentOS 6.9 - MacOSX 10.13

Earliest version tested

Nuke 11.1v5 - This issue no longer appears in this version and has regressed

Expected behaviour
For the file_type to be correct when reading in a file with a write node

Actual behaviour
It changed when the reading knob was enabled