When I create a fresh application, save it to an empty directory, then I am asked for two file names ("project1.lpi" and "Unit1.pas"). But the "Unit1.pas" name is not accepted and I get a warning saying (translated from german):

It looks like a Pascal file.
It is recomended to use non-capital letters for file names to avoid problems.
Rename it?

But the name was chosen by Lazarus itself!
Why did it use a file name that is not recommended and then ask the user whether it should be renamed?

Damned! Again this has been reported (this time 2 year ago):

http://bugs.freepascal.org/view.php?id=14122

The strange thing is, that I did not experience this behaviour with builts half a year ago and older.
I am wondering, why it only appeared recently (but it could also be, that I didn't use the default
names before).

Dunno about the German wording, but IMO it's clear: You can save the file with an all-lowercase name, for compatibility with other platforms, or cased as it is (i.e. like the Unit name). Both versions are acceptable.

DoDi

There exists an option for the Save action of camel cased units: Ask, Do
nothing, or Auto rename.

The strange thing is, that I did not experience this behaviour with builts half a year ago and older.

Maybe you changed the option to "Ask"?

DoDi