Currently only the first bug is linked to the issue tracker, e.g. see https://chrome-internal-review.googlesource.com/c/305259/.

In other words

   BUG= 662140 ,  653198 

should expand into

    BUG=<a href="https://bugs.chromium.org/p/chromium/issues/detail?id=662140" class="style-scope gr-linked-text">662140</a>, <a href="https://bugs.chromium.org/p/chromium/issues/detail?id=653198" class="style-scope gr-linked-text">653198</a>