Uncompressed Lightmaps rendering incorrectly in HTML5

When using uncompressed Lightmaps in HTML5, the lighting is rendered incorrectly. Using (the default) compressed lightmaps, generates no error.

Also reproduced in Main Promotable-CL-2487422 (Enscriptem 1.29.00)

In Editor:

[Image Removed]

In HTML5 (Mozilla NightlyBuild):

[Image Removed]

1. Unzip attached AH_HTML5Lightmaps 4.8.zip
2. Open AH_HTML5Lightmaps.uproject
3. Launch on HTML5 (Mozilla Nightly Build)

RESULTS: See attached images, Lighting seems reversed on certain walls

EXPECTED: Lighting remains the same as in editor