I can reproduce the problem on my Ubuntu 10.10 Maverick x86_64 system (PCManFM 0.9.7, package version 0.9.7-1ubuntu1; it was installed as part of lubuntu-desktop 0.18).

I have *not* been able to reproduce the bug with my Ubuntu 10.10 Maverick i686 system. (I don't think the architecture is the cause of the difference, though.)

I've actually been experiencing this problem for months (at least), but neglected to report it. (Sorry about that!)

This bug (as it manifests on my system) is strange in the following four ways. (When I write of the "usual way" of opening a PCManFM window, I mean creating it by clicking the "File Manager" icon that is present by default in the LXDE Launch Bar provided by lubuntu-desktop. This icon represents the application shortcut "pcmanfm %U".)

(1) If I open a new PCManFM window in the usual way and, in that window, try to add an item to the bookmarks by dragging it in, the window closes, but the bookmark is successfully created.

(2) If I open a new PCManFM window by running the command "pcmanfm" in an LXTerminal and, in that window, try to add an item to the bookmarks by dragging it in, the window does not close (and the bookmark is successfully created). This is highly unexpected, because I am using LXDE (via lubuntu-desktop), so a window created by running "pcmanfm" still belongs to the *original* pcmanfm process. I have checked to verify that this is the case on my system.

(3) If I open a new PCManFM window by running the command "pcmanfm" in an LXTerminal and then, in a PCManFM window opened the usual way (opened either before or after the other one was opened), I try to add an item to the bookmarks by dragging it in, the window does not close (and the bookmark is successfully created).

(4) If I open a new PCManFM window by running the command "pcmanfm" in an LXTerminal, close that window, and then, in a PCManFM window opened the usual way (opened either before or after the other one was opened, and also either before or after the other one was closed), I try to add an item to the bookmarks by dragging it in, the window *does* close (but the bookmark is successfully created).

(5) I am sure I recall a PCManFM window closing a couple of times as a result of *removing* a bookmark (but the removals succeeding). I have not reproduce that systematically, though.

(6) In a local session created by running "ssh -c blowfish -X localhost", if I open a new PCManFM window by running the command "pcmanfm", that window does belong to a new PCManFM process, as expected. In that window, if I try to add an item to the bookmarks by dragging it in, PCManFM does not crash (and the bookmark is successfully created). However, the message "** (pcmanfm:1862): DEBUG: FmJob error: No such file or directory" is printed to the ssh console.

(7) If I create a new PCManFM window from a local ssh session as described above, and then I create a second PCManFM window in the usual way and, in that second window, I try to add an item to the bookmarks by dragging it in, the window *sometimes* closes, and *sometimes* doesn't. Either way, the bookmark is successfully created. When creating the bookmark does not cause the window to close, a debug message like the one quoted above is displayed in the ssh terminal; when it doesn't cause the window to close, no debug message is displayed. Note that this is a debug message being displayed in the terminal that owns the pcmanfm instance that does *not* own the window where the action is occurring. There are other sequences of events that I could test, but adding the third event (starting the ssh -X session) means that there are plenty of them, and I suspect that testing them all would not generate information that would be particular useful when added to what I have already discovered. If someone thinks it would be useful for me to try them (e.g.starting the ssh -X session and creating the PCManFM window the usual way), I'd be willing to do so.

(8) Although no crash report is ever generated, it appears that the PCManFM windows *are* closing due to crashes, since after a PCManFM window is closed as a result of dragging an item into the bookmarks, the process ID for pcmanfm (determined with /usr/bin/pgrep) changes. I have verified on my system that pcmanfm's pid does not normally change when PCManFM windows are opened or closed.

Here's the contents of the file .gtk-bookmarks in my home directory (/home/ek):

file:///media/Wingardium Wingardium
file:///home/ek/Downloads Download
file:///home/ek/Pictures Pictures
file:///home/ek/Videos Videos
file:///home/ek/source source
file:///home/ek/Torrents/Complete Complete
file:///home/ek/Torrents/Incomplete Incomplete
file:///usr/local/src src
file:///home/Shared Shared

The file has a terminating newline, as usual. Its format, according to /usr/bin/file, is ASCII text. If you think doing so would be useful, I can attach it. (I just didn't want to create confusion--people might think it is the file from Pierre's system, which it is not.)

In case it's useful, the output of "uname -a" on my system is:
Linux Apok 2.6.35-23-generic #41-Ubuntu SMP Wed Nov 24 11:55:36 UTC 2010 x86_64 GNU/Linux