ID 363750 - Render output retains file extension even if output path is cleared

Problem summary
Render output retains file extension even if output path is cleared. This occurs when rendering an animation and saving to a new directory rather than the directories specified in the output path.

Customer reported version
modo.n/a

Customer reported platform
10.13

Steps to reproduce
1) Open Modo.
2) Select File>Open and open the provided scene.
3) Selecting the "Shading" tab in the item bin.
4) Select "Final Color Output_exr"
5) Click "Browse" under "Output Filename" and specify an output directory/filename. Make sure to set the file type to "Open EXR Half 16-bit (*.exr)" and select "save."
6) Select and delete all of the text in the Output Filename box.
7) Select render>render animation. Set "Last Frame" to 1. Click "OK."
8) Specify an output filepath and filename. Make sure the filetype is set to "Targa (*.tga)" and click save.
Result: Modo will render the images. The "Final Color Output_exr" file will render as an exr, rather than a targa.

Workaround
Delete the render output and create a new one with the same settings. Do not set an output filename.

Reproduced by support
This bug has been reproduced in:
12.1v2 - Windows 10, OSX 10.13.5
12.1v1 - Windows 10
12.0v1 - Windows 10
11.2v3 - Windows 10
11.2v1 - Windows 10
11.1v1 - Windows 10
11.0v3 - Windows 10
10.2v4 - Windows 10, OSX 10.13.5

Earliest version tested
10.2v4 - Windows 10, OSX 10.13.5 - This issue appears to be in all versions of the product
Expected behaviour
The render output should respect the file type selected in step 8 if the "Output Filename" is empty. 

Actual behaviour
The render output does not respect the selected file type, and renders in the original output filename format despite no prompt to render to this path during rendering.