Topic: Strange strings in urls appear as indexing errors in G. Webmaster Tool

I have noticed in Google Webmaster Tools that there are many errors of indexing my Rails app:

http://MYHOST/kaUnsyUuw4iRjFNGzBm3ezWDLVS pmBEvqdc5D7Gwg= 404 (Not found)   
http://MYHOST/Vd/LvyPNSi 16kj5EwBIPcu40MG/tj4/KgZrmamj s= 404 (Not found)   
http://MYHOST/rfgvF bCmxRtxG7rS/veFS7ife6Pvuo51MM5FFZfrU= 404 (Not found)   
...

Did someone else notice such problem in his application?
No such urls are present in the HTML code and production.log does not contain any (I haven't found at least).

It's weird and annoying...