svn:mime-type with charset in auto-props

Hi,
Is there a way to specify the default mime-type together with charset for
new files in svn config auto-props ?
Setting mime-type from commandline works OK:

svn propset svn:mime-type "text/plain;charset=cp1250" ala.txt

I am trying to set this in config auto-props, like this:

[auto-props]
*.txt = svn:mime-type=text/plain;svn:charset=cp1250

But then each new *.txt files gets two properties:
svn:mime-type=text/plain
charset=cp1250

I tried all kinds of quoting the property value, but nothing worked.
Please let me know if there is a way to do this correctly.

Thanks,
--
Maciek Starzyk