Sentences that don't start with a capital hurt to my eyes. Especially when they're this large:
There's more: the system posts for you sometimes (for the 'possible duplicate' message). These autoposts don't always have a capital, and then it's like I wrote that sentence without a capital. This specific case has been brought up already.
Given the votecounts on that question and the answers (also note the -34 on Jeff's authorative answer - the reason for status-declined), wouldn't it be a good idea to go over all the system messages and capitalize1 them?
From Jeff's answer:
It's not a complete sentence,
True - although not for the 'put on hold'.
so it doesn't need to be capitalized.
Doesn't need to, but people expect it.
We don't capitalize the tabs on the user page, or the homepage, for example.. or, heck, even here on the question page itself.
That's different - they're short slugs, not informational texts.
1: with capitalize I mean let every sentence start with a capital, like you normally do