A file name uFancyControl is much more readable than ufancycontrol. But Lazarus always saves them in lower case. If saved twice with capital letters, then at least in the Editor window the name is shown in the specified caseness, while the file name still is in lower case. Not sure if this a bug or a feature...
An important feature, if you do not only work on Windows.
What would happen without it? Suppose you are on Linux. You create a new form and save the unit as "uForm.pas". The form is used in the mainform; you add the new unit to its uses clause, but write the unit name as "UForm". What will happen? The unit will not be found because a file "UForm.pas" does not exist, the existing file is spelled as "uForm.pas"
With this feature, the unit was automatically saved as lower-case filename, i.e. "uform.pas". When the IDE notices that the file "UForm.pas" does not exist, it automatically searches for the lowercase filename, "uform.pas" - which is found, of course.
Once you fell into this trap, you will never call this feature "annoying" again.