Having calmed down a bit over a coffee and a fag..
Seriously guys, I don't want to denegrade a fine product which I love, so if you want to remove this post and PM me on this matter - that's fine, but when the same set of data can be viewed in one calendar style with absolutely no problem but not in another, when the same set of data appears in the new style calendar in one version but not in another - then something is seriously wrong somewhere. And it's not something you should be expecting your customers to pay for to get fixed.
Further info. Since I have established that with a clean empty test site, I can enter and see entries in the new style calendar, there may be certain characters that are not being handled correctly. I have exported the entire table to a csv (1202 records) and on first run through, the only possible candidates are ' as in O'Connell, + as in Gavin + Stacey, - as in Evening-Group, and : as in Evening:Junior group. These are all in the Subject attribute