During this morning's (4th day Hol Hamo'ed Pesach outside Israel) I noticed that in Numbers 9:2:
וְיַעֲשׂ֧וּ בְנֵי־יִשְׂרָאֵ֛ל אֶת־הַפָּ֖סַח בְּמוֹעֲדֽוֹ׃
’Let the children of Israel keep the passover in its appointed season.
The word "Pesach" which usually has a segol has a kamatz in this case. I know that usually a segol becomes a kamatz on a etnachta and sof pasuk. As you can see, in the above verse, the change is on the tipcha.
None of the standard sommentaries (Mikra'ot Gedolot) explain this anomaly. Is there anyone that (can) explain why the kamatz is here?