Please show us what $cpath actually contains, instead of describing it as "visually the same". See $Data::Dumper::Useqq for how to make Data::Dumper output invisible characters.
the value in a @folders array element:
/media/igor/chmk/home/zamutnii/BackUp/LanBackup/СЭД/FkClnt1/SUBSYS/PRINT/RTF/
the value in %file_system's key:
/media/igor/chmk/home/zamutnii/BackUp/LanBackup/СЭД/FkClnt1/SUBSYS/PRINT/RTF/
the value in $cpath:
/media/igor/chmk/home/zamutnii/BackUp/LanBackup/СЭД/FkClnt1/SUBSYS/PRINT/RTF/
the first two match, but the last one doesn't match with either.
I will check out Data Dumper
Also, consider trying to find out what triggers the "sometimes" situations. You might also want to record more information, like whether $file_system{ $cpath } exists instead of blindly grabbing its value.
I gave examples in my code that I was testing it for existence. A wish to solve what triggers, is exactly, the reason I posted the question, because, I've been trying to solve this problem for a one a half of the day already.

In reply to Re^2: maybe, a corrupt selected entry in Tk::BrowseEntry by igoryonya
in thread maybe, a corrupt selected entry in Tk::BrowseEntry by igoryonya

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