This is a really small thing... but I think every software developer has been there, and it can get pretty frustrating.
If you are a long-time developer, you have most probably experienced it: You encounter a problem (like a really strange error message, or a strange bug with some library that you just can't understand eg. because the documentation of the library is lacking or other reasons) and you try to search for a solution online. Surely others have had the same problem and solved it.
Very often this is so, and you usually find the answer in the first few google hits. Sometimes, however, you will see someone asking the very question you are looking for, and then answering their own post with just "never mind, I found the solution", and never explaining what the solution was. You are left with nothing.
A lesser form of this is when someone asks the question, another person answers it, and the first person just answers with a "thanks, I will try that to see if it works", and never following that up with a report of whether it did work or not. This is, of course, a much more minor form because you can try the solution yourself. However, it's still a bit annoying because if the original poster had reported that the solution works, you would be surer of it before starting to test. (After all, the person who responded could be simply guessing, and be wrong.)
Why not try the solution first, and then thank the person who gave the answer?