ISO-8859-1 as source file encoding and syntax Highlighting.

I have long time problem in Scala Eclipse plugin.
If I open scala source file syntax highlighting is lost.
After editing and saving highlighting comes back.

Today I noticed how this problem is related to source files encoding and
comments.
Traditionally my source files are in ISO-8859-1.

Let’s create simple class.

class Simple {

var alfa = 300 // Comment
}

Save and reopen. Highlighting is OK.
Now change comment.

class Simple {

var alfa = 300 // Comment öüä
}

Save and reopen. Highlighting is LOST.

If I use UTF-8 as source file encoding Highlighting does not disappear even
with ‘ÖÜÄ’ characters.

So, is it possible to use ISO-8859-1 as source file encoding without losing
Highlighting ?

Current configuration:
Eclipse SDK Version: 3.4.2
Build id: M20090211-1700
ch.epfl.lamp.sdt_2.8.0.r17382-b20090326023419.zip

Thanks
Toivo