The part of the sentence "disappointing to learn that" is correct and usable in written English.
You can use it when you are expressing dissatisfaction about something you've found out or someone has told you. For example: It was disappointing to learn that the concert had been cancelled due to unforeseen circumstances.
So it is disappointing to learn that it is not operational.
So it's a little disappointing to learn that it doesn't represent Sylvia's long, rich life, fully lived and cherished.
It is deeply disappointing to learn that the Obama administration is only now about to convene a jobs summit.
But it's disappointing to learn that our small effort is focussed on adopting an approach that didn't work in Iraq and isn't working in Afghanistan.
The Council speaker, Peter F. Vallone, a Democrat from Queens, issued a statement yesterday, saying: "It is disappointing to learn that this law has been overturned.
How disappointing to learn that his hard work and talent may not have been the only factors fueling his performance on the field.
"We'll deal with that but we were told he was going to take up the option and to learn that might not be the case at this late stage is disappointing".
That said, it's still disappointing to learn in hindsight that the media should have done a better job treating the deceased gorilla like a serious contender.
It was a disappointing moment for Turks to learn that the foreign affairs committee of the US House of Representatives has narrowly voted to approve a resolution describing the massacre of more than a million Armenians by the Ottoman Empire during the first world war as genocide.
As disappointing as it was to learn that Einstein didn't pen the letter, it was equally exciting to discover a plethora of documents I hadn't even known existed.
