Dynamic markers overwrite additional marker

Here is a video showing my problem.
Briefly the page as two server connections, one retrieves a single record from a list of universities containing the latitude and longitude of the university
The second connection retrieves all associated accommodation providers with 5 miles, also with lat and lng pre geocoded.
The map displays all the selected accommodation providers on the map and this works perfectly
The map in centred on the lat & lng of the university and that works perfectly.

I also have added one additional marker to show a pin at the universities location based on the same lat & lng as the map centre
This pin shows for a fraction or a second disappears when the accommodation provider marker are drawn on the map

Here is a video of it happening, you will see a purple pin appear for a fraction of a second when the map is refreshed.

mapbug.mp4 (8.9 MB)