Dojo 1.8.1 is the release included with IBM Domino 9.0. If you have XPages applications in your Domino server, maybe, your apps could not work properly in this new release.
You should test your application just in case is not compatible with Dojo 1.8.1.
As a temporary fix, you have the possibility to choose which Dojo release you want to use either at server or database level.
You can set a variable in the Xsp Properties file, that you can find, in Designer 9, under Application Configuration
With this line your XPages app will load dojo 1.5.1. It should be available under \data\domino\js in a folder named \dojo-1.5.1
This feature's been available since Domino 8.5.1. You can find more informatino here.
In any case, you have to take into account that this change could break standar XPages functionality in your application. Test thoroughly before making any changes.