Compiling .less files while having multiple instances of XWiki running, results in strange CSS code

This is a development issue. Not sure if what's the exact problem but the use case is that:

• Having 6.2.2-Snaphot instance open on port 8080
• Having a 6.2 or 6.2.1 instance open on another port (8084)
• Make a change in 6.2.2-Snapshot less folder on forms.less for example
• Go to the running instance and resave a ColorTheme page in order to force the compiler to apply your less change
• You will have strange CSS displayed

I guess maybe there is a name conflict for the files between the two running instances or maybe a process conflict (not sure) that combines .less files from both instances.

On visible bug can be seen in the menus, but the idea is that the changes I made to the forms.less file are not taken into consideration (I've added some vertical-align to an input, for example).

This makes it harder to test and develop in the same time.
In order to find out duplicate issues I needed two instances in order to determine if some code I previously committed didn't fixed also other problems.

If you have just one instance running or if you don't make changes to the .less files, the menus (in this example, but I'm talking about any less change) are displayed ok.