erratic conditional formatting behaviour in Calc

operating system - Kubuntu 13.10
libreoffice version -
Everything’s in English.

I have a spreadsheet which I’m using to learn languages. There are 2 columns which are meant to have conditional formatting: a ‘learnt’ column with the date I learnt a particular word and a ‘revise’ column with the date the next revision is due. The important one is the ‘revise’ column so I’ll focus on that here.
I have 2 formatting rules:
cell value == TODAY()
cell value < TODAY()
If either of these are TRUE, the date in that cell should turn red.

For some time I’ve been missing revisions because the conditional formatting doesn’t always work. Multiple times, I’ve selected the entire revision column, gone to Format > Conditional formatting > Condition and checked that the correct formatting is set, yet this keeps happening. Some of the cells containing today’s date will be highlighted and others won’t be. I even discovered that Libreoffice would tell me all the selected cells had formatting applied, but if I selected a single cell and checked its formatting I’d find it had none applied. I had the opposite experience today, discovering that a cell whose formatting is missing DID have formatting applied.

Another rather bizarre thing: yesterday, after discovering that the formatting was working incorrectly yet again, I selected all my formatted columns and removed all conditional formatting from them, planning to start over. After doing that I discovered libreoffice was interpreting ‘2014’ (which I enter as 14, and which it automatically turns into 2014) as ‘0014’. I swear that wasn’t the case before I deleted the conditional formatting o_o
Anyway, I fixed it with regex and reapplied conditional formatting…SEVERAL TIMES. It still isn’t working properly.

It seems that if I add new formatting rules on top of the existing ones it temporarily fixes the problem (i.e., all today’s revisions become highlighted), but the next day the problem is back.

It seems like a bug, as I had this problem on my old laptop (running Mac OS 10.4.11 and some ancient version of Libreoffice) as well. But if it IS a bug, it’s strange that I haven’t been able to find any mention of it on the web.