here is the command in question (I've also attached a screenshot of the command setup in the bundle editor):

There doesn't seem to be any special pattern, it doesn't always do it and immediately running the command again seems to restore the syntax colouring. Making any further edit to the file also restores the syntax colouring.

I mostly work on Objective-C files, a simple test case would be:

1. open a largish ObjC .m file (say 500+ lines).

2. make an edit, e.g.: unindent a line of code

3. run the command

4. try this a few times

Often I see the code lose its syntax colouring from the point where I made the last edit onwards, sometimes its only the actual line or lines in question. All the affected text goes white, it's as though it has lost its scope although selecting some text in the unhighlighted area and showing the scope reveals a perfectly normal scope list. 

I have seen this behaviour on 3 separate Macs: 2 Mac Pro's and 1 MacBook Pro, running pretty much all of the alphas so far, on Lion 10.7.4.

Hope that helps

Chris