syntax highlighting not correct in bash script

The following shell script is not highlighted correctly.

. % cat foo.sh
#!/usr/bin/bash

UPSTREAM=${1:-'@{u}'}

Please find the screenshot at https://pasteboard.co/HwyXxZU.png .

As you can see in the screenshot, the first and second left curly
braces are blue and yellow while the third and fourth right curly
braces are blue and magenta. Any idea why?

Using vim 8.0, on Debian 9.5 (Stretch).

thanks
raju
--
Kamaraju S Kusumanchi | http://raju.shoutwiki.com/wiki/Blog

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