Step to reproduce:
1) launch mongo shell
2) type 'show dbs'
3) Database names are shown twice in a sporadic manner. Sometimes when you exit the shell and relaunch it it only shows the name once and then it reappears again. In the example below, it shows "platform_asset" twice.

bash-3.2# ./mongo
MongoDB shell version: 1.6.2
connecting to: test
> show dbs
admin
asset
local
platform_asset
platform_asset   
test
>