Excel VSTO recognizers not able to be enabled

[Mark]

We have developed a pair of VSTO add-ins for excel and word with similar
functionality including a set of 3 VSTO smart tags that are added to the
VstoSmartTags collection during the add-ins Startup event.
On word there are no problems but when we go in to the excel proofing >
autocorrect > smarttag options we are finding that the checkboxes to
enable/disable individual smarttags are acting oddly, with changing state of
one or more checkboxes effecting different ones instead, or having no
apparent effect at all.

E.G.

Smarttags list:
1) Custom Tag 1 (VSTO Recognizer) - Checked
2) Custom Tag 2 (VSTO Recognizer) - Not Checked
3) Custom Tag 3 (VSTO Recognizer) - Not Checked
4) Financial Symbol (Smart tag lists) - Checked
5) Person (Outlook Email Recipients) - Checked

If we check custom tags 2 & 3, and uncheck the financial symbol tag, press
OK, then open the window again, what we get is

1) Custom Tag 1 (VSTO Recognizer) - Checked
2) Custom Tag 2 (VSTO Recognizer) - Not Checked
3) Custom Tag 3 (VSTO Recognizer) - Not Checked
4) Financial Symbol (Smart tag lists) - Checked
5) Person (Outlook Email Recipients) - Not Checked

Any help anyone could offer would be much appreciated

Many thanks in advance

Mark