Yes I can reproduce it. It works correct in tclsh85, but not in tclsh86.
<pre>
>tclsh85
% set volumeList [string tolower [file volumes]]
c:/ d:/
% set element [lsearch -exact $volumeList "c:/"]
0
% lindex $volumeList 0
c:/
% set volumeList
c:/ d:/
% exit

>tclsh86
% set volumeList [string tolower [file volumes]]
c:/ d:/
% set element [lsearch -exact $volumeList "c:/"]
-1
% lindex $volumeList 0
C:/
% set volumeList
c:/ d:/
%
</pre>