The mapping for > setup by xmledit interferes with Vim's method of adding the same text via a blockwise visual selection.
Using <C-v>…I (Ctrl-v, selecting a region (e.g. the first column of multiple lines), then uppercase i), you can insert text and the visual selection will get replaced with it on each line after pressing Esc.
Given the mapping used by xmledit, the Esc in there aborts the insert process:
inoremap <buffer> > <Esc>:call <SID>InsertGt()<Cr>
It would be nice, if the plugin would work without leaving insert mode (via Esc).
As a workaround, you can use <LocalLeader>> to insert the greater than sign.