Might it be better if each error is separated on its own line, just for readability? For example:
The following templates contained errors and were not saved:
1) Template tags are not well-formed. <xen:comment> was not closed.
1) Template tags are not well-formed. <xen:comment> was not closed.2) another error
I assume considering it uses numbering that it reports multiple errors where possible. This helps to see each error as its own individual error, instead of reading a paragraph of text to outline the reported errors.