menus crashed in rss-poster 0.7.6

I have a multi-layer structure nav-menu,in my testing,it crashed when i fetch any rss feed.
for example:
nav-menu structure:
1
2
3
-3_1
–3_1_1
–3_1_2
-3_2
–3_2_1
–3_2_2
-3_3
4

after i fetch any rss feed:
the top nav-menu will gone.
nav-menu structure:
1
2
3_1
3_1_1
3_1_2
3_2
3_2_1
3_2_2
3_3
4
all will be top-level menu.

http://wordpress.org/extend/plugins/rss-poster/